• Effects of weight reduction on serum levels of lipids and apolipoproteins were measured in 13 obese children (seven girls, six boys). Mean weight loss of 8.4% of the initial body weight was achieved after 4 weeks of energy intake restriction and exercise. Serum total cholesterol (5.46±1.01 mmol/L) and triglyceride (2.08±0.52 mmol/L) levels were significantly high compared with control values before treatment and were significantly reduced to 4.32±0.75 and 1.31 ±0.42 mmol/L, respectively, after treatment. Serum high-density lipoprotein cholesterol level (1.03±0.23 mmol/L) was significantly low and unchanged after treatment (0.94±0.25 mmol/L). Serum apolipoprotein A-I level (0.039±0.009 mmol/L or 111 ± 0.26 g/L) was normal before treatment and significantly reduced, to 0.032±0.007 mmol/L or 0.92±0.19 g/L, after weight reduction. Serum apolipoprotein B level (0.00019±0.00007 mmol/L or 1.07±0.21 g/L) was significantly high before treatment and decreased to the normal range after treatment (0.00014±0.0009 mmol/L or 0.76±0.24 g/L). The ratio of apolipoprotein B to apolipoprotein A-I (1.09±0.29) was significantly high on admission and decreased significantly to 0.64±0.12 after treatment. Serum apolipoprotein E level (0.0014±0.0006 mmol/L or 0.05 ±0.02 g/L) was normal and decreased to 0.0008±0.0002 mmol/L or 0.03±0.01 g/L after treatment. In conclusion, weight reduction achieved by energy intake restriction and exercise had beneficial effects on serum lipid and apolipoprotein concentrations for the prevention of future atherosclerosis.