To investigate the role of nitric oxide (NO) in steroid-induced femoral head necrosis, NO production was measured indirectly as nitrite in serum and synovial fluid samples from patients with steroid-induced femoral head necrosis together with serum samples from healthy volunteers matched for age and sex. The results showed that:① serum nitrite concentration in patients with femoral head necrosis were significantly lower than that in controls (P＜0.001); ② nitrite level of synovial fluid was markedly higher than that of serum. In addition, there was a positive correlation between them (r＝0.378,P＜0.05). We reach the conclusion:① NO is synthesized by synovium and chondrocytes; ② the decreased NO concentration in serum suggests a protective role in steroid-induced femoral head necrosis.