California Association of Toxicologists proficiency testing program.

A proficiency testing program that has been conducted by the California Association of Toxicologists for 10 years is described. The purpose of the program is to allow each participant the opportunity to evaluate their methodology and efficiency on a qualitative as well as quantitative basis with other laboratories in the organization. The program is conducted entirely on a volunteer basis with the sample prepared by a different member each time. The selection of drugs for inclusion in the sample, the preparation and distribution, and the collation and dissemination of the results are discussed. An evaluation of all aspects of the program is presented.