AbstractChanges in renal excretions of sodium (Na), potassium (K), and chloride (CI) upon a postural change from sustained recumbency to standing and walking were examined in 146 children with chance proteinuria and/or hematuria and in 27 children with biopsy‐proved diffuse mesangial proliferative glomerulonephritis (GN) including membranoproliferative GN (MPGN). Renal excretions of Na, K, and CI were inhibited in children with macroscopic hematuria and/or proteinuria and in those with moderate to severe mesangial proliferative GN and MPGN. Reductions in urinary Na/K ratios, reflecting the effect of aldosterone on renal tubular reabsorption, were noted upon a postural change, but there was no significant relation between the changes in urinary Na/K ratios and glomerular lesions. These results suggest that renal excretions of Na, K, and CI are simultaneously decreased upon an orthostatic postural change in children with severe mesangial proliferative GN and MPG