The biochemical development of whole brains from male and female miniature swine aged 2 weeks to 1 year was studied. The data were similar for both sexes. The brain-body weight ratio declined rapidly for the first 10-12 weeks after birth, then decreased at a slower rate up to 1 year. Total brain lipid weight and lipid phosphorus changed rapidly during the first 8-10 weeks of life, but thereafter changed very little. The glycolipid content rapidly increased during the first 12-14 weeks of life and then increased at a slower rate. Total brain cholesterol increased continuously over the time period studied, although the rate of increase appeared to decline with age. Monogalactosyl diacylglycerol concentration remained constant up to about 8 weeks of age, but then decreased continuously up to 1 year. The alkali-labile fatty acid composition of pig brain remained relatively constant except for increases in 18:1 and 22:6(n - 3) and a decrease in 16:0. The increase in percentage of 18:1 was most rapid during the first 10 weeks of age. These data suggest that the "growth spurt" or active myelination phase of miniature pig brain development ends at 8-10 weeks post partum.