Summary A simple paper strip test for the detection of cycloserine and pyrazinamide in the urine is described. It gives positive results with minimal concentrations of 20 μg./ml. cycloserine and 30 μg./ml. pyrazinamide respectively. Clinical trials revealed that after a single dose of 0·25 g. cycloserine the patient's urine gives a positive reaction within 1 to 6 hours after the drug was administered. Similarly, a dose of 0·5 g. pyrazinamide gives a positive reaction within 1 to 8 hours.