In attempt to evaluate the vitamin D status of the infants of our area under the mode of prophylaxis of carential rickets actually used in France, serum 25 hydroxyvitamin D (25 OHD) levels were measured in 65 infants (age 3 - 32 months) during their hospitalisation for acute illness. Most infants were receiving vitamin D either in daily doses (1,200 - 1,600 u) or in unique loading doses (200,000 - 600,000 u every 4 - 6 months). With this prophylaxis serum concentrations of 25 OHD were elevated, i.e. above 75 nmol/l, in more than 50% of the infants, reaching 474 nmol/l in one case. Calciuria estimated by the calcium/creatinine urinary ratio tended to increase in parallel with the serum 25 OHD level. From these data it is concluded that the actual prophylaxis of carential rickets in France frequently uses excessive doses of vitamin D and that new rules have to be established.