This paper describes radiochemical microassays for determining the activities of choline acetyltransferase (ChAc) and acetylcholinesterase (AChE). The methods involve the use of radioactive substrates and specific extraction techniques to isolate and quantify the products of these enzymes. For ChAc, the assay is based on the reaction between labelled acetyl-CoA and choline to produce labelled acetylcholine, which is then extracted and measured. For AChE, the assay involves the hydrolysis of labelled acetylcholine to produce labelled acetate, which is also extracted and quantified. The methods were tested with samples from various nervous tissues and purified enzymes. The results showed that the activities of ChAc and AChE could be accurately measured using these methods, with blank values corresponding to activities in 20 ng and 5 ng of brain tissue respectively. The methods are sensitive and suitable for submicrogram quantities of tissue. The use of radioactive substrates allows for accurate and sensitive measurement of enzyme activities. The methods involve the separation of labelled acetylcholine from other radioactive substrates and by-products using techniques such as precipitation with reineckate, sodium tetraphenylboron, or electrophoresis. The methods were compared and found to be effective for determining enzyme activities in various tissues. The results showed that the activities of ChAc and AChE could be accurately measured using these methods, with the blank values corresponding to activities in 20 ng and 5 ng of brain tissue respectively. The methods are sensitive and suitable for submicrogram quantities of tissue. The use of radioactive substrates allows for accurate and sensitive measurement of enzyme activities. The methods involve the separation of labelled acetylcholine from other radioactive substrates and by-products using techniques such as precipitation with reineckate, sodium tetraphenylboron, or electrophoresis. The methods were compared and found to be effective for determining enzyme activities in various tissues.This paper describes radiochemical microassays for determining the activities of choline acetyltransferase (ChAc) and acetylcholinesterase (AChE). The methods involve the use of radioactive substrates and specific extraction techniques to isolate and quantify the products of these enzymes. For ChAc, the assay is based on the reaction between labelled acetyl-CoA and choline to produce labelled acetylcholine, which is then extracted and measured. For AChE, the assay involves the hydrolysis of labelled acetylcholine to produce labelled acetate, which is also extracted and quantified. The methods were tested with samples from various nervous tissues and purified enzymes. The results showed that the activities of ChAc and AChE could be accurately measured using these methods, with blank values corresponding to activities in 20 ng and 5 ng of brain tissue respectively. The methods are sensitive and suitable for submicrogram quantities of tissue. The use of radioactive substrates allows for accurate and sensitive measurement of enzyme activities. The methods involve the separation of labelled acetylcholine from other radioactive substrates and by-products using techniques such as precipitation with reineckate, sodium tetraphenylboron, or electrophoresis. The methods were compared and found to be effective for determining enzyme activities in various tissues. The results showed that the activities of ChAc and AChE could be accurately measured using these methods, with the blank values corresponding to activities in 20 ng and 5 ng of brain tissue respectively. The methods are sensitive and suitable for submicrogram quantities of tissue. The use of radioactive substrates allows for accurate and sensitive measurement of enzyme activities. The methods involve the separation of labelled acetylcholine from other radioactive substrates and by-products using techniques such as precipitation with reineckate, sodium tetraphenylboron, or electrophoresis. The methods were compared and found to be effective for determining enzyme activities in various tissues.