1. A water-soluble croconazole glucuronide was isolated from the urine of rabbits dosed intravenously with croconazole, using XAD-2 column chromatography, reversed-phase RP-8 column chromatography and h.p.l.c. 2. beta-Glucuronidase hydrolysis liberated unchanged croconazole from the glucuronide. 3. Secondary ion mass spectra, i.r. and n.m.r. spectroscopic studies, including two-dimensional n.m.r. techniques (ROESY and HETCOR), showed the metabolite to be a quaternary ammonium glucuronide of croconazole: i.e. a chemical bond exists between a nitrogen, having sp2 type orbital, in the imidazole ring of croconazole and the anomeric carbon of glucuronic acid. 4. The urinary excretion of the glucuronide amounted to 2.8 +/- 0.7% of dose (mean +/- SD, n = 4) in rabbits.