A mortality study of garment industry workers exposed to formaldehyde (50000) was conducted. The purpose of the study was to evaluate the human carcinogenicity of formaldehyde. The cohort consisted of 256 decreased workers, 192 female, reported to a death benefit insurance fund for three shirt manufacturing factories where cloth pretreated with formaldehyde containing resins was used. The underlying causes of death were determined. Proportionate mortality ratios (PMRs) and proportionate cancer mortality ratios (PCMRs) were computed. Prior industrial hygiene sampling at two of the facilities found 0.1 to 1.0 part per million formaldehyde. No deaths due to nasal cancer were observed. Statistically significant excesses in mortality were observed for cancer of the buccal cavity, biliary passages and liver, and other lymphatic and hematopoietic sites, the respective PMRs being 750, 313, and 400. The PCMRs for cancers of the buccal cavity and other lymphatic and hematopoietic sites were 682 and 342, respectively. Cancer of the biliary passages and liver was still in excess, but not statistically significant, PCMR being 274. When stratified by sex and race, white females had statistically significant excess mortality due to cancer of the buccal cavity and other lymphatic and hematopoietic categories. When stratified by latency and duration of exposure, statistically significant excess mortality occurred for all malignancies combined for cancer of the buccal cavity, biliary passages and liver, and for all lymphatic and hematopoietic sites, and other lymphatic and hematopoietic sites for subjects with more than 10 years of latency and duration of exposure. The authors suggest that because of the small number of deaths, the findings should be regarded as tentative. Conclusions as to the human carcinogenicity of formaldehyde must await the results of more definitive investigations.