The findings of the Los Angeles County Street Drug Identification Program over the period from 1971 to 1980 for analysis of 1163 samples of street drugs represented as stimulants are presented. Of the 614 alleged cocaine samples, cocaine was found to be absent in 19.2%, found combined with stimulant substitutes in 22.5%, and found by itself in 58.3% of these samples. The validity for 473 alleged amphetamine samples was only 27.1%, with 23.0% of samples found to contain stimulant substitutes along with amphetamine, and 49.9% of the samples lacking any of the alleged drug. Seventy-six alleged methamphetamine samples showed 32.9% validity, with 3.9% of samples having mixtures of alleged drug and substitutes, and 63.2% of samples lacking any methamphetamine. A total of 15 different stimulant substitutes were found in 74 combinations. Caffeine, ephedrine, lidocaine, and procaine were the commonest substitutes.