Assays of sperm penetration into cervical mucus, in the configuration of double-ended tests (DETs), are an accepted format for evaluating the efficacy of sperm-directed contraceptives in mucus. In order to distinguish relative contributions of compound permeation into, and com pound bioactivity within, cervical mucus with respect to vanguard sperm penetration measured in DETs, direct measurements were made of concentration profiles of the spermicide nonoxynol-9 (N9) after diffusion into mucus-filled capillary tubes. N9 was dissolved in two different delivery solutions, deionized water and saline, in an attempt to exploit a Donnan-mediated swelling of mucus for enhanced delivery of the spermicide. Average diffusion coefficients, 7 and 5 x 10(-7) cm(2)/sec for N9-water and N9-saline, respectively, indicate that the diffusion of NP, a surfactant material, is governed by the size of the N9 micelle rather than the molecular size, in the concentration range typically found in commercial preparations. Permeation of N9 into mucus was significantly greater for water versus saline as delivery solution, although the difference was slight. A more pronounced difference between the two treatments was found in DET results, due to an osmotic and/or pH activity of the delivery solution itself against sperm in mucus. (C) 1997 Elsevier Science Inc.