In this study, the ultrastructural observations in rat kidneys were studied 2, 24 and 48 h after intravenous injection of 1, 3 and 9 g iodine per kg body of ioxaglate and iohexol. The effect of the contrast media was mainly on the proximal convoluted tubule cells, the presence of vacuoles containing granular and membranous structures was a striking feature. In the distal convoluted tubular cells, pycnotic nuclei and cytoplasmic bulges toward the lumen were observed. In some glomeruli, membranous structures in cytoplasm of podocytes and thickening of glomerular basal membrane were seen. Values of biochemical analysis were slightly higher especially at high doses in experimental groups when compared to the control. The results suggest that iohexol causes more degeneration than ioxaglate. Not only proximal convoluted tubule cells but also the other parts of the nephron were affected by contrast media.