The effects of low intensity endurance training on skeletal muscle capillary density and serum lipoprotein levels were studied in 11 non-obese men (18-25 years). The subjects performed a 6-week training regimen (60 min, 5 times per week) at the lactate threshold (LT). Capillary density was determined in biopsy specimens obtained from the vastus lateralis muscle before and after the training. The number of capillaries per fiber (cap/fiber ratio) before training was 1.97±0.47, and increased to 2.49±0.69 after training (p<0.05). The maximal oxygen uptake (VO₂ max) and LT-VO₂ increased significantly by 5% (p<0.01) and 27% (p<0.01), respectively, whereas no change was observed in body weight. Low density lipoprotein cholesterol (LDL-C) tended to decrease (p=0.06). The change in the cap/fiber ratio correlated inversely with the change in the ratio of LDL-C to high density lipoprotein cholesterol (HDL-C) (r=−0.61, p<0.05). It was also positively associated with the change in HDL₂-C (r=0.82, p<0.01) and inversely associated with the change in HDL₃-C (r=−0.63, p<0.05). The change in LT-VO₂ was inversely associated with the change in LDL-C (r=−0.62, r<0.05). These results indicate that low intensity training increases capillary density in skeletal muscle, which may explain in part the changes in the lipoprotein profiles.