The purpose of this study was to determine the effect of carrier vehicle on the penetration of brevetoxin ([3H]PbTx-3) into skin layers and receptor fluid. Disks of guinea-pig skin were mounted on penetration chambers. Epidermal surfaces were dosed with 0.320 microgram/cm2 of PbTx-3 dissolved in 50 microliters of vehicle [water, methanol, or dimethylsulfoxide (DMSO)]. In vitro skin penetration by PbTx-3 during 24 hr of exposure was 6.2, 2.3 and 26% for water, methanol, and DMSO, respectively (expressed as % of dose applied).