Reticulocytes production index was determined in 63 pregnant women and in 96 patients. The results show that 86% of the pregnant women, who were registering their pregnancy for the first time, were anaemic. There was significant reticulocytopenia in all the anaemic pregnant women and in the patients. Erythropoiesis was found to be depressed in all subjects patients by two to seven times those expected in normal responsive bone marrows. There was no correlation of the bone marrow impairment with parity of the pregnancy. The bone marrow impairment was more pronounced during the 16th week of gestation and less so in older pregnancies. Malnutrition and infection (especially malaria) are suggested as the aetiological factors of the bone marrow depression of erythropoiesis.