The effect on pain and heat sensation of monomere non-ionic contrast media with different osmolality was assessed in a randomized double-blind study. Peripheral angiography was performed in 29 patients who suffered from chronic occlusive vessel disease. The two non-ionic contrast media iomeprol and iopentol were applied intraindividually. The contrast media with an iodine concentration of 350 mg/ml had an osmolality of 618 or 810 mosm/kg. A contrast medium volume of 80 or 90 ml was injected in the abdominal aorta. The mean flow was 13.9 ml/s. The two contrast medium injections were separated by an interval of 10 min. No analgesic premedication was given. The pain and heat intensity was semiquantatively measured using a visual analogue scale ranging from 0 (no heat/pain) to 100 (intractable heat/pain). The median after the first injection was calculated as 40 for iomeprol and 70 for iopentol. The comparison of heat and pain sensations after the second injection showed a less distinct difference with a scale rating of 60 for iomeprol and of 65 for iopentol. The statistical variance was highly significant (p < 0.01) in favor of iomeprol.