The effect of infection by Chlamydia pneumoniae (C pneumoniae) and Helicobacter pylori (H. pylori) on patients with coronary heart diseases (CHD) was investigated. 40 patients; 20 suffered from acute myocardial infarction (AMI) (Group I) and 20 suffered from angina (Group II) were selected as patient groups. 20 clinically heaJthy persons of the same age were selected as a control group (Group III) . The patient groups were subgrouped according to the most important risk factors for CHD (smoking, hypertension, and hypercholesterolaemia). The level of C pneumoniae IgG & IsM and H. pylori IgG were detected in the sera of the three groups. It was found that C pneumoniae IgG was positive in 18%, 14%, and 4% with mean titre 364.8,380.7, 12.8 (in groups I, II, and III respectively) which was significanly higher in group I and II than group III. C pneumoniae IsM was negative in groups I and III, while it was positive in 15% of group II with mean titre 275.6 with a statisticaJ significance among the three groups. H. pylori IgG was positive in 60%, 50%, and 45% with mean concentration 312.2, 315.4, and 151.3 on groups I, II, and III (respectively) with insignificant difference among the three groups. As regards to smoking status, C pneumoniae IgG was higher in smokers than in non smonkers in groups I and II with significant difference in group I only. C pneumoniae IsM was insignificant in both groups. H. pylori IgG was high in smokers in both groups with non significant difference. Concerning blood pressure, C. pneumoniae IgG, IsM and H. pylori IgG in both groups were high in hypertensives with no significant relation amOlIg them. As regards to cholesterol level, the mean titres of C pneumoniae IgG and IsM were high in hypercholesterolaemic patients in both groups with no significant relation among them, while the mean concentration of H. pylori IgG was high in hypercholesterolaemics in both groups with a significant difference in group I only. We concluded that, infection with C. pneumoniae and to a lesser extent H. pylori may playa role in the pathogenesis ofCHD and their treatment may enhance the recovery of the disease.