The article presents a comprehensive research protocol for evaluating temperature regulation in field-active ectothermic animals, particularly lizards. The protocol requires data on body temperatures (T_b), available operative temperatures (T_o), and the thermoregulatory set-point range (T_set). These data are used to estimate several quantitative indexes: the "precision" of body temperature (variance in T_b), the "accuracy" of body temperature relative to the set-point range (average difference between T_b and T_set), and the "effectiveness" of thermoregulation (extent to which body temperatures are closer to the set-point range than operative temperatures). Additional data on thermal performance can also be used to estimate the impact of thermoregulation on performance. The authors critique traditional measures of temperature regulation, such as variance of T_b and regression slope, which are shown to be flawed. They propose new indexes that provide a more detailed and quantitative portrait of thermoregulation. A sample analysis of three Anolis lizard species in Puerto Rico demonstrates the utility of the new protocol and its superiority to previous methods. The methodology is general and can be applied to other ectotherms and environmental factors. The article also discusses potential extensions of the approach, including the estimation of the physiological impact of temperature regulation and the consideration of dynamic diel shifts in thermoregulatory demands.The article presents a comprehensive research protocol for evaluating temperature regulation in field-active ectothermic animals, particularly lizards. The protocol requires data on body temperatures (T_b), available operative temperatures (T_o), and the thermoregulatory set-point range (T_set). These data are used to estimate several quantitative indexes: the "precision" of body temperature (variance in T_b), the "accuracy" of body temperature relative to the set-point range (average difference between T_b and T_set), and the "effectiveness" of thermoregulation (extent to which body temperatures are closer to the set-point range than operative temperatures). Additional data on thermal performance can also be used to estimate the impact of thermoregulation on performance. The authors critique traditional measures of temperature regulation, such as variance of T_b and regression slope, which are shown to be flawed. They propose new indexes that provide a more detailed and quantitative portrait of thermoregulation. A sample analysis of three Anolis lizard species in Puerto Rico demonstrates the utility of the new protocol and its superiority to previous methods. The methodology is general and can be applied to other ectotherms and environmental factors. The article also discusses potential extensions of the approach, including the estimation of the physiological impact of temperature regulation and the consideration of dynamic diel shifts in thermoregulatory demands.