Primer3Plus is an enhanced web interface for the Primer3 primer design program, designed to be more user-friendly and intuitive compared to the original Primer3 interface. It addresses the limitations of the original interface, which can be confusing for occasional users due to its extensive options and settings. Primer3Plus uses modern web technologies and has been developed in collaboration with molecular biologists and technicians. It focuses on specific tasks, hides detailed settings until they are needed, and includes functionalities for automating tasks like designing primers for cloning or sequencing. Users can store settings and designed primer sequences locally, and selected primers can be sent to an order form for laboratory integration. The interface supports common sequence formats and allows for easy expansion or integration of external software. The open-source Perl source code is available under the GPL license from SourceForge, and Primer3Plus is accessible at http://www.bioinformatics.nl/primer3plus.Primer3Plus is an enhanced web interface for the Primer3 primer design program, designed to be more user-friendly and intuitive compared to the original Primer3 interface. It addresses the limitations of the original interface, which can be confusing for occasional users due to its extensive options and settings. Primer3Plus uses modern web technologies and has been developed in collaboration with molecular biologists and technicians. It focuses on specific tasks, hides detailed settings until they are needed, and includes functionalities for automating tasks like designing primers for cloning or sequencing. Users can store settings and designed primer sequences locally, and selected primers can be sent to an order form for laboratory integration. The interface supports common sequence formats and allows for easy expansion or integration of external software. The open-source Perl source code is available under the GPL license from SourceForge, and Primer3Plus is accessible at http://www.bioinformatics.nl/primer3plus.