Steroids are still the mainstay of therapy in primary chronic glomerulonephritis (PCGN), regardless of underlying disturbance or pathology. Moreover, relationship between known abnormalities and disease manifestation is stochastic, therefore treatment continues to be empirical. It is not known whether responsiveness is related to immune phenotype. We performed flowcytometric lymphocyte (Ly) phenotyping (CD19, CD3, CD3CD4, CD3CD8, CD56/16) on 16 patients (pts) (12M, 4F), mean age 37.6+/-13 years with primary chronic glomerulonephritis (PCGN): minimal change disease (MCD)--6 pts, focal and segmental glomerulosclerosis (FSGS)--4 pts, mesangial proliferative glomerulonephritis--5 pts, mesangiocapillary glomerulonephritis--1 pt, before and at 7 days of oral Prednisone 1 mg/kg/day (in 2 divided doses). Before steroids: 4/16 pts(25%) had elevated BP; 9/16(56.2) showed nephrotic proteinuria. Serum creatinine was >1.2 mg% in 6/16(37.5%). At 7 days WBC count increased (13,079.37+/-4966.4/microl vs. 8021.25+/-2077.4/microl; p=0.0007), Ly percentage (%) decreased (20.30+/-9% vs. 29.9+/-10.4%; p=0.0095), while absolute (abs.) Ly count remained unchanged. Both CD19 Ly% and CD19 Ly abs. count increased (16.13+/-6.5% vs. 9.52+/-3.7%; p=0.0015, and 410.012+/-29.7/microl vs. 223.56+/-123.8/microl; p=0.0077, respectively). NK (natural killer)% decreased (9.15+/-5.2% vs. 14.19+/-7.1%; p=0.0296). CD3, CD3CD4, CD3CD8 Ly subsets and CD4/CD8 ratio showed no change. Variation in proteinuria (2.88+/-2.1 g/24 h vs. 3.45+/-1.7 g/24 h; p=0.4) did not reach statistical significance (Wilcoxon-Mann-Whitney). In 11 pts we performed an additional analysis at 1 month. Compared to levels before steroids, there was an increase in WBC, CD19 Ly% and CD19 Ly abs. count and a decrease in NK% and NK abs. count. Other Ly subsets and CD4/CD8 ratio remained unchanged. Variation in clinical parameters (proteinuria, serum Creatinine, BP) did not reach statistical significance. Changes in Ly profile precede changes in clinical parameters and thus are divergent. While our patients proved to be early non-responders, further studies to elucidate whether profile changes provide for response specification are warranted.