Mutations of the N- and K-ras genes occur in approximately 15-30% of acute myeloid leukaemia patients. The role of the oncogenic ras in leukaemogenesis remains unclear. Few studies have revealed that mutations in the ras oncogene family are more probably found in acute myeloid leukaemia patients with previous exposure to toxic agents. A case-case study was conducted in the areas of Florence and Turin, Italy, to investigate whether the presence of N- and K-ras mutations in acute myeloid leukaemia patients was related to a higher frequency of exposure to chemicals. During a 3-year period, 111 acute myeloid leukaemia patients were enrolled. All the patients were interviewed using a semi-structured questionnaire collecting data on residential history, occupation, personal habits and pathological history. The presence of N- and K-ras mutations was analysed by amplification and synthetic oligonucleotide probes and by the so-called polymerase chain reaction amplification for specific alleles technique. A total of 34 (30.6%) patients were found to harbour ras mutations in N-ras and/or K-ras. Fourteen patients (12.6%) had a single ras mutation and 20 patients (18%) had two ras mutations. A positive association between a priori at risk jobs and ras mutations was found, based on nine exposed cases; the odds ratio, adjusted by age, sex and previous X-ray and/or chemotherapy was 2.8 (95% confidence intervals: 0.9-9.0). When considering only subjects with two ras mutations the odds ratio was 4.8 (95% confidence intervals: 1.2-18.8). The odds ratio for a previous X-ray and/or chemotherapy was 16.2 (95% confidence intervals: 1.8-755.9); when only subjects with two ras mutations were considered, the odds ratio was 26.1 (95% confidence intervals: 2.5-1248.9). In conclusion, our data suggest that ras oncogene mutations might identify a group of leukaemia in people with previous X-ray/chemotherapy or with exposure to chemical agents in the work environment.