A procedure for the measurement of pregnanetriol in urine by gas chromatography is described. The internal standard is added to the standards, controls and unknowns prior to the enzymatic hydrolysis of the steroid conjugates. Next, the hydrolyzed steroids are extracted from urine and converted to the volatile trimethylsilyl ether derivatives prior to gas chromatography. The initial addition of the internal standard appears to compensate for all procedural losses in this rather complex procedure. The intra- and interassay coefficients of variation at a level of 1.3 mg per liter were 5.3% and 11.8%, respectively. The method is linear to a pregnanetriol:internal standard ratio of 0.871. The analytical recovery for the method was 103 +/- 10.2%.