OBJECTIVE To elucidate the extent of nephrotoxicity of long-term occupational exposure to styrene. METHODS In all 10 styrene-exposed workers (employed, mean age 12.6 years) and 15 nonexposed workers were studied. Each participant collected multiple overnight and end-of-shift urine samples. The sum of the urinary concentrations of mandelic acid and phenylglyoxylic acid (MAP) was determined to assess the absorbed dose of styrene. The urinary parameters alanine aminopeptidase (AAP), beta-galactosidase (beta GAL), N-acetyl-beta-D-glucosaminidase (NAG), retinol-binding protein (RBP), and albumin (ALB) were determined to assess the effects on renal function and integrity. RESULTS The median concentration of MAP in urine was 175 mg/g urinary creatinine (CREAT-U; range 72-496 mg/g). The 8-h time-weighted average (8-h TWA) exposure to styrene was estimated from the urinary concentration of MAP and ranged from 21 to 405 mg/m3. RBP showed a borderline correlation with the dose of styrene. ALB in end-of-shift urine samples showed a borderline correlation with the absorbed dose of styrene. CONCLUSIONS From the borderline correlation of RBP with the dose of styrene it was concluded that there might be a slight effect on the tubuli. The borderline correlation of ALB with the dose of styrene, together with the observation that five values were above the reference limit of the laboratory, suggests an effect on this parameter.