Levels of volatile N-nitrosamines were measured in 10 brands of latex and 2 brands of silicone catheters using high performance liquid chromatography. The cytotoxicity of catheters from identical batches was determined by measuring the inhibitory effect of catheter extracts on the uptake of 3H-labelled thymidine into L-929 fibroblasts in culture (IC50). The most frequently encountered nitrosamines were N-nitrosodi-n-butylamine and N-nitrosodiethylamine. Total N-nitrosamine levels in excess of 100 ng/g were found in 6 of the 16 catheters tested. When compared with the cytotoxicity of the catheters a significant correlation was found, with increasing nitrosamine content being associated with greater cytotoxicity. In view of the reported toxic and carcinogenic effects of these compounds it is suggested that the nitrosamine content of catheters be routinely monitored and safe regulatory limits be imposed.