The 25-hydroxyvitamin D concentration (25-OHD) in maternal and cord blood of 192 mothers was determined at delivery from June to the end of November. Ninety-nine mothers had received a daily supplementation of 12.5 micrograms of vitamin D during pregnancy and this group had a significantly higher 25-OHD concentration both in maternal and in cord blood than in the corresponding non-supplemented group. A daily supplement of 2.5 micrograms of vitamin D was given to 63 of the mothers during lactation. Of these mothers 44 were still lactating after 6 months. The dietary vitamin D intake of 31 mothers was calculated. We found a significant correlation between the maternal serum 25-OHD concentration 16-18 weeks after delivery and the total vitamin D intake. The intake (5.5 micrograms/d, including supplementation) was lower than that recommended for lactating mothers which is 10 micrograms/d (Food and Nutrition Board, 1980).