Serum levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D have been determined in 65 Saudis, 45 white and 12 dark-skinned non-Saudis. The subjects were healthy male blood donors and living in Riyadh (latitude 24 degrees), Saudi Arabia for more than one year. A high percentage of the studied population were found to have low serum levels and to be at risk of developing vitamin D deficiency. Serum levels of 1,25-dihydroxyvitamin D were normal. Avoidance of sunshine is probably the main factor contributing to vitamin D deficiency in Saudi Arabia. Encouragement of exposure to sunlight and fortification of food with vitamin D are indispensable measures for improving the vitamin D status of the population of Saudi Arabia.