Normal human skin fibroblasts and cells from 2 benign (3T3 and 3T6B) and 1 malignant (3T6D) fibroblast lines were grown in the presence of C20 fatty acids in the concentration range 0-100 mg/l culture medium. The culture medium consisted of 10% FCS and 90% DMEM, the cells were dosed with various concentrations of fatty acid in ethanol as carrier 24 hours post-trypsinisation, and the viability determined using Trypan Blue exclusion after a further 48 hours. The threshold between cytostatic and cytotoxic effects was considered to be that concentration of fatty acid which limited cell number to that of the controls at the end of the post-trypsinisation recovery period. All the fatty acids exhibited growth limitation potential, to a greater or lesser extent, which varied dependent on the degree of unsaturation of the molecule and transformation of the fibroblasts. In general, the effects appeared more likely to be related to the role of fatty acids in phosphoglycerides, rather related to the role of fatty acids in phosphoglycerides, rather than via eicosanoid metabolism.