Uptake efficiencies of the gills of English sole (Parophrys vetulus) for four homologous phthalic acid esters were directly measured and compared with octanol-water partition coefficients (K sub ow). Test compounds were diethyl phthalate (DEP), butylbenzylphthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP), and di-n-octyl phthalate (DOC). Mean uptake efficiencies in a single pass through the gills were 11% for DEP 42%, for BBP, 3% for DEHP, and 12% for DOC. Uptake efficiencies for DEP and BBP were inversely correlated with weight-specific ventilation volume and did not correlate with aqueous concentration. Uptake efficiencies for DOC and DEHP were uncorrelated with any measured parameter.