A new thin-layer chromatographic procedure for the detection of the antihypertensive/diuretic drug hydrochlorothiazide in human urine is described. The sensitivity of the method, 5 micrograms/mL, makes it useful to both the clinician interested in determining patient compliance and the toxicologist who must identify or confirm hydrochlorothiazide ingestion. The rapidity of analysis typically allows the screening of 25 urine samples within one hour.