The presence of Chlamydia pneumoniae infection was examined in 66 patients with unstable angina pectoris (UAP), 155 patients with acute myocardial infarction (AIM) and 112 controls without signs of a heart disease. Besides evaluation of anamnestic data, ECG and coronarographic examination, serologic examination of C. pneumoniae by the microfluorescent method anti-MOMP and ELISA of anti-LPS of globulin IgA and IgG serum classes in every patient was performed. Moreover, in patients with UAP, routine biochemical methods for the detection of total cholesterol levels and its lipoprotein fractions LDL, HDL and triacylglycerols were used. The levels of anti-MOMP C. pneumoniae antibodies and anti-LPS of the IgA class in sera of patients with UAP were statistically highly significantly increased (chi 2 = 19.54; chi 2 = 12.92; p < 0.01) and anti-LPS of the IgG class significantly increased (chi 2 = 6.15; p < 0.05) in comparison with controls. It can be assumed that the participation of C. pneumoniae is aetiologically possible. Total cholesterol levels, LDL, HDL and triacylgylcerols were increased above the normal range in 34.8%, 48.5%, 39.4% and 28.8% of patients, respectively. The anti-LPS C. pneumoniae ELISA test of globulin class IgA in patients with UAP seems to be the most suitable method for the determination of infections with C. pneumoniae.