We investigated the effects of hyperbaric oxygenation (HBO) on ischemic osteonecrosis and on ossification disturbance of the femoral heads in growing, spontaneously hypertensive rats (SHR). 10 male SHRs aged 5 weeks (Group A) and another 10 male SHRs aged 8 weeks (Group B) were treated with HBO at 2.8 atmosphere absolute (ATA) for 6 weeks in a total of 30 hours. The control animals, 10 male SHRs (Group C) and 10 male wistar Kyoto rats (WKY, Group D), were kept under normal laboratory conditions. All the rats were killed at the age of 17 weeks for microscopic examination. In Group A, there was no evidence of osteonecrosis, and only 2 femoral heads with ossification disturbance were observed. In Group B, there were 2 femoral heads with osteonecrosis and 1 with ossification disturbance. In contrast, there were 6 femoral heads with osteonecrosis and 4 with ossification disturbance in Group C. It was concluded that HBO prevented osteonecrosis and ossification disturbance of the femoral heads in SHR.