By the use of transmission electron microscopy (TEM) and energy dispersion spectrometry the amount (mean value mean = 191 +/- 94 fibers/mg of tissue) and the type (chrysotile and tremolite) of asbestos fibers have been determined in tissue samples of four bladder cancer patients affected by pulmonary asbestosis, working in the same plant producing asbestos-cement pipes and boards. Similar measurements were carried out on samples of bladder cancers of eight control patients not professionally exposed to asbestos. Only five of them also revealed chrysotile fibers (mean = 151 +/- 196 fibers/mg of tissue). The paucity of the study and control cases and the small quantitative difference between them regarding the presence of infraneoplastic asbestos fibers does not consent us to hypothesize a causal relationship between tumor and occupational exposure.