Partitioning of free styrene glycol in plasma and packed red blood cells was investigated in this study. Allyl benzene glycol was synthesized and used as an internal standard in the procedure. It was determined there was no significant difference in the styrene glycol concentrations in the plasma and red blood cells layers (B=0.08, SE=1.01) of dosed blood samples. This result suggested that free styrene glycol distributes uniformly throughout whole blood. The plasma layer was chosen for analysis in this study and free styrene glycol concentrations were determined in 85 plasma samples using the developed methodology of this study. Samples and exposure data were obtained from three reinforced plastic industry companies in the state of Washington. The exposure data investigated were: eight-hour air styrene concentrations, whole blood styrene concentrations and urinary metabolite (sum of mandelic and phenylglyoxylic acids) concentrations. Companies #1,2 and 3 afforded the following number of plasma samples, respectively: 31,17 and 17. Fourteen and six replicate measurements and sets of exposure data were obtained for Companies # 1 and 2, respectively, approximately one year after initial monitoring. Statistical analysis regressing exposure data and plasma styrene glycol concentrations against exposure data for single and replicate observations are presented in this work. Our findings vary depending upon the company sampled. Company # 3 produced statistically significant relationships in every regression. Companies # 1 and 2 did not.