This paper describes standard mortality and nested case-control analyses of colorectal cancer for a cohort of synthetic textiles workers in which a cluster of five cases was observed previously. The cohort consisted of 7,487 men and 2,724 women who had more than 1 year's experience at the plant and who were either working in 1947 or were newly employed between 1947 and 1977. The Standardized Mortality Ratio (SMR) for colorectal cancer for men was 0.69 (95% confidence interval (CI): 0.52-0.92; 50 deaths) and for women it was 1.02 (95% CI: 0.57-1.69; 15 deaths). Among men only there was a suggestion that risks increased according to the length of service at the plant. In the nested case-control study, incident cases as well as deceased cases were included. A variety of analyses were carried out according to duration of employment in the processing units. For men the risk of colon cancer increased with duration of employment in the polypropylene and cellulose triacetate extrusion unit (unadjusted odds ratio (OR) for ≤5 years duration = 5.52; 95% CI: 1.12-27,26; 4 exposed cases). It was not possible, however, to provide an independent confirmation of this putative association because the case series included three of the original five cases. There was some evidence of increased risks in the cellulose acetate fiber manufacturing unit and in the dyeing and finishing unit, but the data were compatible with the null hypothesis of no effect. No associations were observed for employment in any of the other processing unit.