It has been documented that sex hormone may play a role in the pathogenesis of murine lupus. To determine the effect of tamoxifen (TAM) on NZB/W F1 female mice, a total dose of 800 microg (22 mg/kg body weight) of TAM was administered subcutaneously every 2 weeks. The control mice were injected with peanut oil only. After treatment with TAM for 5 months, the mice were killed and immunological parameters were evaluated. The results suggest that NZB/W F1 mice treated with TAM had less severe proteinuria and increased survival rate compared to controls. Flow cytometric analysis of splenocytes revealed a significantly lower percentage of B cells and CD5+ B cells in the TAM-treated group. There was a significantly lower serum level of soluble tumour necrosis factor (TNF) receptor I and II molecules in the TAM-treated mice. Immunohistological study showed that control mice had severe immune complex deposition in the kidney. In contrast, TAM-treated mice had much less pathological change. In summary, this study demonstrated that TAM treatment might be able to alleviate the symptoms of lupus nephritis, influence B-cell count, modulate the expression of cytokine receptors and thereby subsequently affect immune function. Further studies to determine the cellular mechanisms in lupus nephritis may increase our understanding of this complex disease and provide additional targets for therapeutic intervention.