Four experiments on 76 female and 79 male rats were performed in which we followed up the effect of four weeks' administration of estradiol benzoate (Agofollin Depot 1 mg per rat once a week or 5 mg per kg once every 5 days s. c.) and testosterone isobutyrate (Agovirin Depot 25 mg per kg once every 5 days s. c.) on the local circulation in the tibia and distal femur (by means of 85 Sr-microsphere uptake) and on bone density and ash weight related to bone volume. Local circulatory values increase in the bones after oophorectomy (OOX) and orchidectomy (ORX) and decrease after estradiol in sham-operated rats of both sexes; testosterone inconstantly reduces the 85Sr-microsphere uptake in the bones of sham-operated male rats. Estradiol decreases local circulatory values in OOX females and ORX males to the level observed in sham-operated animals. Testosterone has a similar inhibitory effect in ORX males as estradiol; less pronounced, but statistically significant lowering occurs also in the tibia of OOX females. Density of the tibia and ash weight related to bone volume unit falls after OOX and ORX and rises constantly after estradiol; after testosterone administration, it does not change in sham-operated rats and OOX females, but rises in ORX males. Probably the most important finding is that also testosterone reduces local circulation in the bones of rats, though less regularly and less markedly than estradiol (in the dosage used).