A retrospective analysis of white blood cell (WBC) counts and fibrinogen levels was performed on 292 consecutive patients admitted to the emergency department for chest pain likely due to ischaemic heart disease. Aims of the study were to evaluate their utility in discriminating between cardiac and non-cardiac chest pain, and to identify those "chest pain-enzyme negative" patients who are at high risk of developing acute myocardial infarction (AMI). The results obtained showed that WBC (p < 0.0001) and fibrinogen (p < 0.0001) significantly discriminated AMI patients. However, only male gender (p < 0.03), abnormal CK-MB% (p < 0.0001) and neutrophil counts (p < 0.0001) were independently related to AMI. The combined determination of neutrophils and CK-MB% increased the sensitivity from 50% (for CK-MB% alone) to 70% (p < 0.05), with a negative predictive value similar to that observed for CK-MB% alone. These results suggest that determination of neutrophil counts might help to improve the accuracy of AMI diagnosis in emergency patients.