Eighty-five clinical urine samples and nineteen urine samples previously found by other laboratories to suggest genetic metabolic defects were prepared for trimethylsilylation by treatment with urease, followed by azeotropic dehydration. The "Target Analyte Search" program provided with the VG Trio 2 gas chromatograph-mass spectrometer required 6 min to quantify 103 compounds relative to endogenous urinary creatinine. This technique has been used to confirm diagnoses including cystinuria, lysinuria, medium-chain acyldehydrogenase deficiency, ornithine transcarbamylase deficiency, aspartylglucosaminuria, methylmalonic, propionic and glutaric acidurias.