This study examined the utility of thin layer chromatography (TLC) for detection of recent use of opioids and benzodiazepines among drug addicts seeking treatment at the Drug Dependence Treatment Centre of All India Institute of Medical Sciences, New Delhi, India. Over a period of 5 years (1991-1995), 6,055 urine samples were analyzed for opioids (morphine, codeine, buprenorphine, dextropropoxyphene, pentazocine) and benzodiazepines (diazepam, nitrazepam) by TLC. Out of all the drug tests (n = 9,922) carried out, 24% of the drugs had been used during the past 72 hr. Averaged across all drugs, the detection rates corresponding to 24, 48, and 72 hr by TLC were 37%, 36%, and 31%, respectively. A high percentage of negative TLC results was observed in these samples. Moderate sensitivity of the TLC assay procedure, low consumption of drug, short time between drug use and urine collection, overreporting by the subjects, and drug use history of the subject obtained from multiple sources led to high negative results. These findings suggest that all the TLC negative results also need further confirmation by an alternative, more sensitive technique in a clinical setting. This will make the drug abuse testing program more meaningful.