Eight dermal absorption experiments (two in vivo; six in vitro) and one intravenous experiment were conducted using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) either neat (high dose at approximately 250 microg/cm(2) and low dose at 10 ng/cm(2)) or sorbed on a low organic soil (LOS) or high organic soil (HOS) at 1 ppm (10 ng TCDD/10 mg soil/cm(2)). After 96 h the percent of applied dose absorbed (PADA) for the neat low dose was 78% in vivo (rat) and 76% in vitro (rat). PADA for the equivalent TCDD dose sorbed on LOS were 16.3% (rat in vivo), 7.7% (rat in vitro) and 2.4% (human in vitro). The PADA for TCDD sorbed on HOS (1 ppm) was 1.0% (rat in vitro). Generally, rat skin was observed to be three to four times more permeable to TCDD than human skin. At steady state, the dermal flux of TCDD in neat form, sorbed on LOS at 1 ppm, and sorbed on HOS at 1 ppm (all in vitro, rat) was 120, 0.007, and 0.0007 ng/cm(2)/h, respectively (ratio = 1.7 x 10(5):10:1). Making adjustments to account for differences between in vitro and in vivo results and adjusting for application to monolayer loads, the 24-h TCDD absorption for human skin is estimated as 1.9% from LOS (1 ppm) and 0.24% from HOS (1 ppm).