The influence of DMSO (dimethyl sulfoxide) on foliar absorption and translocation of herbicides and plant membrane permeability was investigated. Primary leaves of bean (Phaseolus vulgaris L., var. Black Valentine) were treated with ¹⁴C-labeled DMSO, 3,6-dicholoro-o-anisic acid (dicamba), 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat) and 2-choloro-4(ethylamino)-6-(isopropylamino)-s-triazine (atrazine). DMSO at concentrations of 25% or more caused by varying degrees of acute toxicity. However, ¹⁴C was generally distributed throughout the plant 5 days after application of DMSO-¹⁴C, as determined by autoradiography and counting. DMSO, 30%, was not as effective as 0.25% Tween 80 (non-ionic surfactant containing polyoxyethylene sorbitan monooleate) in enhancing the absorption and translocation of dicamba, a phloem-mobile herbicide. Tween 80 was more effective than DMSO in enhancing the foliar uptake of atrazine and distributing it within the treated leaves. The contact toxicity and apoplastic movement of paraquat was increased with DMSO. Spectrophotometric studies revealed the absorption spectrum of paraquat was shifted by addition of DMSO. Root uptake of KH₂³²PO₄ by corn (Zea mays L., var. VPI 646) was inhibited by 3% or higher DMSO. Treatments of DMSO reduced oxygen uptake in corn roots. DMSO failed to increase diffusion of labeled solutes through isolated plant cuticular membranes. In Beta vulgaris L. (beet) permeability studies, DMSO increased efflux of betanin from root cells. Combining atrazine with DMSO resulted in a greater increase in membrane permeability. Membrane permeability of corn mitochondria as determined by characteristic swelling and shrinkage was unaffected by DMSO.