The aim of this study was to examine whether physical and chemical working conditions explain the association of social class with ischaemic heart disease (IHD). We investigated the issue in a cohort of 2974 males aged 53-75 years (mean 63) free from overt cardiovascular disease. Potential confounders included were: alcohol consumption, physical activity, tobacco smoking, serum cotinine, serum lipids, serum selenium, body mass index, blood pressure, hypertension, social class, and retirement status. During the follow-up period (1985-1986 to 31 December 1991), 184 men (6.2%) had a first IHD event; 44 events were fatal. Compared to higher social classes (classes I, II and III), lower classes (classes IV and V) had a significantly increased risk of IHD (P < 0.05); the age-adjusted relative risk (RR) with 95% confidence limits was 1.44 (1.06-1.95), P = 0.02. Mean who had been occupationally long-term exposed (> or = 5 years) to either soldering fumes or organic solvents had a significantly higher risk of IHD than unexposed: RRs were 2.1 and 1.7, respectively. After adjustment for all the above potential confounders and including also these two occupational factors, the RR of low social classes was reduced to a non-significant 1.24 (0.87-1.76), P = 0.24, i.e. by 45%. Adjusting for non-occupational factors only reduced the RR from 1.44 to 1.38 (1.0-1.90), P = 0.05, i.e. by about 14%. Assuming that the association of soldering fumes and organic solvents with risk of IHD was causal, it was estimated that 16% of IHD cases in low social class could be ascribed to these exposures.(ABSTRACT TRUNCATED AT 250 WORDS)