Ten healthy, adult mongrel dogs were each given various dose levels of sodium iothalamate IV, and postinjection radiographs were made. Base-line plasma and urine osmolality, glomerular filtration rate, packed cell volume, plasma protein concentration, serum urea nitrogen concentration, serum creatinine concentration, and urine specific gravity were measured. The base-line values and the dose of contrast medium were compared statistically with linear and density measurements made from the post-injection radiographs. Base-line plasma osmolality was directly related to the pyelographic and nephrographic density. The dose of contrast medium directly influenced the kidney length, the kidney, pelvic, diverticular, and ureteral widths, and the renal and diverticular densities despite variations in base-line values within accepted limits.