Transdermal permeation of trisodium phosphonoformate (PFA) alone and in presence of sorption promoters, dimethylacetamide (DMAC), N-N-diethyl-m-toluamide (NNDEMT) and 1-dodecylazacycloheptan-2-one (Azone) was studied using excised rat skin. DMAC in concentrations between 0.05% to 10% had no effect on amount of PFA in the skin or permeated across skin, flux or lag time. 10% NNDEMT doubled the amount of PFA in the skin, increased fourfold the amount permeated across the skin, and increased the flux fivefold. There was no influence on lag time. Azone doubled the amount of PFA in the skin, more than tripled the amount permeated across the skin, and increased the flux fourfold. There was no influence on lag time.