We describe an inductive coupled plasma-optical emission spectroscopic method to determine silicon in spot urine specimens. A 6-fold standard addition series of the urine specimen ranging from 0 to 356 micromol/l silicon was applied, and the method meets the requirement of matrix compensation in a frequently changing environment. The inter-assay variation was +/-3.0%, intra-assay variations for three specimens were +/-1.7%, +/-1.1% and +/-0.84%. To compensate for physiological variations of urine density, the silicon concentrations in urine were related to urinary creatinine which was measured in parallel by reversed-phase HPLC. Urinary silicon concentrations were examined in 43 healthy controls from the local population. The 5th-95th percentile was 12.6-237 micromol/mmol creatinine. A follow-up of three people over a period of 14 days showed that intra-individual variations of urinary silicon concentrations were smaller than variations between individuals, especially when silicon is related to creatinine.