Percutaneous absorption of ((14)C) monosodium methanearsonate (MSMA) and disodium methanearsonate (DSMA) was investigated in female B6C3F1 mice from a variety of exposure conditions, including aqueous solution, solid compound, and soil. These chemicals are sodium salts of methanearsonic acid, an in vivo metabolite of inorganic arsenic compounds, and are present in water and soil. Permeation experiments were carried out in vitro for 24 h using previously clipped dorsal skin (area = 0.64 sq cu) in flow-through cells with Hepes-buffered Hanks' balanced salt solution as receptor fluid. Applied doses of 10, 100, and 500 micrograms were studied in selected vehicles and dermal absorption was quantified by determining the radioactivity in the receptor fluid and skin following skin surface wash to remove unpenetrated compound. Both MSMA and DSMA exhibited similar dermal absorption from different media and the rank order was: aqueous solution > solid compound > soil. The degree of ionization of the compounds did not appear to affect their skin absorption as both monobasic and dibasic forms penetrated mouse skin to the same extent from aqueous vehicles. An alteration in the aqueous donor volume (20, 100, and 250 microliters) did not significantly change the total absorption of the chemicals, however, larger volumes significantly prolonged the time to reach maximal permeation rates. Thus, dermal exposure to MSMA and DSMA from aqueous solutions poses significantly greater risk for absorption than from soil.