Excised femoral and iliac artery segments have been examined with 20 MHz intravascular ultrasound followed by histological assessment. During the ultrasound examinations, radio-frequency (RF) data were recorded digitally, and used for calculating local values of attenuation slope throughout the tissue, using a frequency-domain technique. The RF data were also reconstructed as conventional ultrasound images, and the attenuation-slope information presented as a threshold colour overlay. Areas identified as degenerative plaque in the histological assessments were usually found to correspond to areas of high attenuation slope, and were clearly identified from the pattern of colours on the combined image. Some examples are presented, illustrating the appearance of various pathologies imaged by this technique.