We measured the serum levels of soluble HLA class I antigen (sHLA-I) to evaluate the immune status of uremia and following renal transplantation. Twenty-one hemodialysis (HD) patients had serum samples collected for sHLA-I analysis before and after HD and also during the initial posttransplant period. The serum sHLA-I levels in patients undergoing HD were higher than in the normal controls (574.8 +/- 431.1 vs. 415.6 +/- 256.1 ng/ml, p < 0.05). In the HD patients, HD duration was not correlated with serum sHLA-I levels (r = 0.01, p > 0.05), and pre- and post-HD serum sHLA-I levels were not significantly different (574.8 +/- 431.1 vs. 568.3 +/- 398.4 ng/ml, p > 0.05). After successful renal transplantation, the serum sHLA-I levels decreased significantly (574.8 +/- 431.1 vs. 226.7 +/- 202.8 ng/ml, p = 0.0001) but increased significantly during the rejection period as compared to the prerejection period (642.8 +/- 296.1 vs. 305.5 +/- 194.7 ng/ml, p = 0.0002). In conclusion, sHLA-I levels are stable in uremic status and can be used as a parameter for monitoring acute graft rejection in renal transplantation.