Background/Aims: Proteinuria in idiopathic minimal lesion nephrotic syndrome (IMLNS) is presumed to be due to the effect of circulating factors on glomerular permeability to plasma proteins. This study examines the expression of messenger ribonucleic acid (mRNA) for cytokines thought to mediate glomerular inflammation during different stages of the nephrotic syndrome. Methods: Messenger RNA expression and stability from peripheral blood mononuclear cells of IMLNS patients in relapse and in remission, and age matched normal controls were measured using a ribonuclease protection assay (RPA). The spontaneous and Interleukin 2 (IL-2) stimulated mRNA expression were studied. Results: Spontaneous mRNA expression for Interleukin 8 (IL-8) from IMLNS patients in relapse was significantly increased when compared to IMLNS patients in remission and normal controls (p < 0.05). After 14 h of IL-2 stimulation, mRNA IL-8 levels expressed by IMLNS PBMC patients in remission were not different from those observed in normal controls. However, after 5 days of PBMC incubation, a significant increase in mRNA for IL-8 in IMLNS patients compared to controls was found (p < 0.01). Stability assay demonstrated that IL-8 mRNA transcript from the nephrotic patients remained higher than those from controls and showed a significantly prolonged life t<sub>1/2</sub> (p = 0.02). Conclusions: IL-8 mRNA expression is increased in IMLNS patients in relapse. Moreover, stability studies show that IL-8 mRNA life t<sub>1/2</sub> is prolonged due to altered post-transcriptional regulation. This finding may explain the elevated serum IL-8 levels observed in these patients during relapse and may have pathogenic significance since IL-8 has been shown to induce proteinuria in the experimental animal.