In a recent joint European research project "Biomonitoring of human populations exposed to genotoxic environmental chemicals: biomonitoring of styrene exposed individuals", a logbook method for assessment of long-term styrene exposure was applied in two Danish factories manufacturing glass fibre-reinforced polyester The method was based on work process identification, assignment of work process concentrations and logbook keeping Measures of exposure calculated by this method were compared with results from simultaneous measurements of styrene in blood and the metabolites mandelic acid and phenylglyoxylic acid in urine Correlations were comparable with those obtained by use of personal samplers as published in the literature Styrene in blood, however, only correlated with logbook concentrations at the time of sampling Exposures were moderate to low Mean personal 8-h time-weighted average concentration ( 8 h TWAC) was 76 mg/m 3 styrene (SD 54 mg/m 3 , range 2-230 mg/m 3) The Danish 8 h TWAC threshold limit value for styrene in air, 105 mg/m 3 ( 25 ppm), was exceeded on 17 % of personal days The summed urinary metabolites, mandelic acid and phenylglyoxylic acid, had a mean personal value of 138 mg/g creatinine (SD 84 mg/g creatinine) on the day of sampling Blood styrene mean value was 129 ltg/l (SD 74 jig/l, range 66-358 gtg/l) It is concluded that the logbook method offers a technique for testing whether measurements are performed on representative days and may be recommended as a tool supplementary to biological monitoring in the assessment of long-term exposure.