P.H. has been reported as having a good prognosis except in some cases of IgA mesangial deposition (MGN-A) with focal segmental sclerosis and proliferation (FSS) which may progress to ESRD. HLA, lymphocytes bearing surface IgA (SIgA), serum immunoglobulins (Ig) and renal histopathology were evaluated in patients with P.H. persisting > 6 months. HLA-A, B and C were determined in 49 patients (29 MGN-A and 20 MGN-non A) and in 524 controls. In P.H. patients the frequency of Bw35 was 43% (similar in MGN-A and MGN-non A) and 23% in controls (p<0.01). Dr7 was present in 8/22 MGN-A (36%) but only in 19/109 (17%) control subjects. SIgA was elevated in 41/42 (98%) patients but only in 3/52 (6%) controls (p <0.001). Mean serum IgA and IgM levels were higher in P.H. patients compared to controls. Of 10 Bw35 patients with MGN-A, 9 had FSS (3 of the 9 evolving to ESRD) compared to 8/19 withoug Bw35 (p <0.01). It is concluded that 1) HLA-Bw35 is present and SIgA elevated more frequently in patients than in controls, and may be useful in separating P.H. from other hematurias, 2) a positive correlation of these findings with FSS and/or progression to ESRD exists only in MGN-A patients, 3) Dr7 seems increased in MGN-A patients, and 4) some P.H. patients require renal biopsy for better assessment of prognosis.