BACKGROUND: Since evidence of a long-term association between routine blood count (Coulter) variables and coronary heart disease (CHD) is inconsistent, the authors analysed white blood cell count (WBC), red blood cell count (RBC), haemoglobin (Hgb), packed cell volume (PCV) and platelet count for their long-term associations with CHD mortality in the first Northwick Park Heart Study (NPHS-I). NPHS-I has follow-up information for >30 years on 2167 White men and 941 White women and holds entry and follow-up data on haematological variables and other known CHD risk factors. METHODS: Proportional hazards Cox models were fitted to estimate rate ratios (RRs) for the separate and joint effects of entry and follow-up Coulter variables. RESULTS: Entry RBC, PCV and Hgb were significant risk factors for CHD mortality after adjustment for gender but only PCV remained significant after adjustment for potential confounders [RR per 1 standard deviation (SD) increase = 1.17, 95% confidence interval (CI) 1.00-1.37]. This effect was partly reduced when the values of 6 years were analysed (RR per 1 SD increase = 1.10, 95% CI 0.93-1.30). No significant gender, smoking or age/time interactions were identified. PCV was the only significant predictor when all Coulter variables were studied jointly. CONCLUSION: PCV was found to predict CHD mortality even after controlling for classical risk factors. This may give some insight into possible mechanisms, such as an influence on thrombin production.