The nature of changes in the lipid profile caused by an acute infection is controversial. The aims of the present study were to study the changes in plasma lipids and lipoproteins in community-acquired pneumonia, to determine whether these changes differ according to the aetiologica/agents, and finally to observe the behaviour of these lipoproteins six months later. Sixty patients, aged between 18 and 87 years, admitted during the period September 1992 and April 1993 with suspected community-acquired pneumonia, were included in the study. Fifty-three of the patients completed the 15-day follow-up investigation, and 37 remained available for study for up to 6 months. On admission and at 15 and 180 days, analyses were carried out for total cholesterol, HDL cholesterol, apolipoproteins A1 and B, triacylglycerols and transaminases. Student's t test for parametric variables was used for statistical analysis, and the Mann-Whitney test for non-parametric variables. The concentrations of total cholesterol (4.2 +/- 1.0 vs 5.5 +/- 1.3 mmol/1), HDL cholesterol (0.9 +/- 0.4 vs 1.2 +/- 0.3 mmol/l), apolipoprotein A1 (0.80 +/- 0.25 vs 1.15 +/- 0.28 g/l) and apolipoprotein B (0.77 +/- 0.28 vs 0.95 +/- 0.28 g/l) showed significantly lower values during the acute infectious process. These analyte concentrations became stable after 15 days with the exception of HDL cholesterol which continued to increase until 6 months (1.2 +/- 0.3 vs 1.3 +/- 0.3 mmol/l, p < 0.01). Patients with non-viral atypical pneumonia showed, on admission, higher triacylglycerol values (1.8 +/- 0.8 vs 1.3 +/- 0.9 mmol/l, p < 0.01) and lower HDL cholesterol values (0.6 +/- 0.3 vs 1.0 +/- 0.4 mmol/l, p < 0.03). Values of aspartate aminotransferase (112 +/- 117 vs 23 +/- 11 U/l, p < 0.001), alanine aminotransferase (127 +/- 141 vs 24 +/- 16 U/l, p < 0.02) and gamma-glutamyl transferase (113 +/- 158 vs 33 +/- 25 U/l, p < 0.03) were higher in the subgroup of non-viral atypical pneumonia. In conclusion, patients with community-acquired pneumonia present a significant decline in total cholesterol, HDL cholesterol and apolipoprotein A1 and B concentrations. Lower concentrations of HDL cholesterol are maintained up 15 days. Patients with non-viral atypical pneumonia present on admission significantly higher triacylglycerol and lower HDL cholesterol values. Those with non-viral atypical pneumonia also present higher transaminase values.