In young non-exercised rats, plasma triglyceride and plasma phospholipid levels increased in summer and low density lipoprotein cholesterol (LDL-C) increased in winter. As for lipids samples from the wall of the aorta, total cholesterol, cholesteryl ester and triglyceride decreased in summer and phospholipid decreased in winter. Exercise diminished the gain in body mass (delta m) and suppressed seasonal changes in the levels of LDL-C and plasma triglyceride. Seasonal changes in the aorta lipids in this case were similar to those found in non-exercised animals. The values of total energy intake (Q) and of delta m.Q-1 were found to change with season in both non-exercised and exercised rats. Seasonal changes in plasma and in aorta lipids observed in these animals ran in parallel with the respective levels of delta m.Q-1 and/or of Q. The training effect on the lipid values detected in summer and/or in winter was also found to be dependent on the reduction in delta m.Q-1 with exercise. In the non-exercised and in the exercised animals, plasma phospholipid was associated with aorta phospholipid and inversely related to aorta cholesteryl ester and aorta triglyceride. The relationship between these estimations suggests that an increase in the plasma phospholipid in summer would remove non-polar lipids from the walls of the aortae.