A method for the determination of cocaine content in coca leaves (Erythroxylum coca) has been developed. The procedure involves refluxing the powdered leaves in 95% ethanol for 15 minutes, followed by acid-base partitioning with chloroform and a GLC assay. The recovery of cocaine was quantitative. This procedure was applied to determine cocaine content in three samples of Erythroxylum coca Lam. collected from different geographic locations in Peru. Using androst-4-ene-3,17-dione as the internal standard the calibration curve was linear over a factor of 0.5 to 10 fold cocaine concentration relative to internal standard. The slope (b) was 0.733, the coefficient of determination (r2) was 1.00 and the average precision was 3.9%.