SUMMARYGestating female pigs received either a low or a high intake per day of diets containing either a low or high protein concentration. A change in the composition of both diets occurred after 2 years, when the protein quality of the high protein diet was improved and the energy content of both diets was increased. Vitamin A determinations were carried out on 245 piglet livers and 32 pairs of kidneys and lungs at birth from 47 sows. The livers, kidneys and lungs of 16 sows were also analysed for vitamin A after approximately 4 years on experiment. Vitamin A was detected at birth with antimony trichloride in the liver of the piglet, but not in the kidney or lung. The sow's kidney was found to contain only small amounts and lung tissue only traces.A dietary vitamin A level of 4800 i.u./kg during the breeding life of healthy sows, or 8600 i.u./day during gestation, was adequate from the point of view of both a constant storage in piglet livers at birth over eight to ten parities and a relatively high concentration remaining in sow livers after that period. This conclusion is in line with recommendations of the Agricultural Research Council (1966).As a consequence of differences in both the condition of the sows and in their responses in the two periods, the results for each period are presented separately. In the first 2-year period, when the sows received a relatively low intake of dietary protein during gestation (between 248 and 317 g protein/sow/day), and a low energy intake; that is, when protein was used for energy production, the liver vitamin A storage of the piglet at birth was increased by raising either the daily protein intake during gestation to 352 g, or the food intake from 1·8 to 2·3 kg/sow/day. Liver vitamin A and N concentrations were negatively correlated with liver weight, but increasing dietary protein concentration raised liver weight and its vitamin A content. Liver vitamin A per piglet was not affected by litter size.A conclusion may not be drawn concerning the contribution of dietary energy to the differences in response between periods, because in addition to dietary changes other differences occurred between periods. Nevertheless, in the second 2-year period, when energy intake during gestation was adequate for normal growth and development, a difference of 150 g in protein intake/sow/day (363 g against 208 g) had no effect on liver weight or its vitamin A content. Furthermore, there was no significant treatment effect on total protein or albumin concentrations in the serum of the sow.