ANALYSES WERE MADE BY RADIOIMMUNOASSAY, ENZYME MULTIPLIED IMMUNOASSAY TECHNIQUE, GAS-LIQUID CHROMATOGRAPHIC, AND THIN-LAYER CHROMATOGRAPHIC TECHNIQUES, WHICH HAVE RESULTED IN 100 PERCENT ACCURACY AS MONITORED BY BOTH STATE AND FEDERAL GOVERNMENT QUALITY CONTROL PROGRAMS. ALL DRUGS REPORTED AS POSITIVE WERE IDENTIFIED BY AT LEAST THREE METHODS, SO THAT FALSE POSITIVE RESULTS WERE ELIMINATED. A TOTAL OF 27.2 PERCENT OF THE URINE SPECIMENS CONTAINED CONFIRMABLE LEVELS OF ONE OR MORE OF THE DRUGS FOR WHICH TESTS WERE MADE, WITH ABOUT 33 PERCENT OF THOSE FOUND POSITIVE CONTAINING MORE THAN ONE DRUG; 7 SPECIMENS CONTAINED AS MANY AS 5 DIFFERENT DRUGS, AND 172 DRUG COMBINATIONS WERE FOUND. OPIATES AND BARBITURATES COMPOSED NEARLY 60 PERCENT OF THE DRUGS DETECTED; MORPHINE WAS BY FAR THE MOST COMMON DRUG FOUND, BEING PRESENT IN 1 OUT OF EVERY 11 SAMPLES. THIS IS PROBABLY DUE TO ITS GREATER USE, SLOW EXCRETION FROM THE BODY, AND METABOLISM FROM CODEINE. METHADONE, PHENOBARBITAL, CODEINE, AND PROPOXYPHENE WERE ALSO FREQUENTLY FOUND. THE DATA INDICATE A TREND OF CONTINUED DRUG USE BY MANY LOS ANGELES COUNTY PROBATIONERS ASSOCIATED WITH PRIOR DRUG PROBLEMS. ALTHOUGH SOME DRUG USE IS UNDOUBTEDLY BY LEGITIMATE PRESCRIPTION, MUCH OF IT IS ILLICIT, CONSTITUTING VIOLATION OF PROBATION CONDITIONS. TABULAR DATA AND REFERENCES ARE PROVIDED. (RCB)