An useful renal biopsy should be representative, that is should contain a sufficient number of glomeruli. However, a non-representative biopsy could possibly provide some information. The aim of the study was to evaluate the relationship between interstitial expansion, glomerular sclerosis and renal function in such material. The material consisted of 28 renal biopsies containing less than 5 non-sclerosed glomeruli. For each case the percentage of completely sclerosed glomeruli was recorded. The relative interstitial volume was evaluated by point counting method. Clinical data as sex, age, serum creatinine and urea levels were included into analysis. The mean percentage of completely sclerosed glomeruli was 39.6%; mean relative interstitial volume was 29.6%. Creatinine level was strongly correlated to relative interstitial volume (R = 0.70), but the correlation of creatinine level to percentage of sclerosed glomeruli was much weaker (R = 0.38). The relationship between interstitial expansion and renal function is seen also in deficient biopsy material. The correlation of renal function with interstitial expansion is stronger the correlation of renal function with glomerular sclerosis. These findings can indicate that the better representation is responsible for stronger prognostic impact of interstitial lesions