Purpose : Irradiation has been shown to be effective in preventing restenosis after dilatation in human peripheral arteries. We have developed a dedicated system for coronary intraarterial irradiation using a 90Y pure beta-emitting source inside a specially modified angioplasty balloon. This paper presents a preliminary dosimetric evaluation of this system. Methods and Materials : Specially fabricated titanium-covered and activated yttrium wires (outer diameter 0.32 mm) were used for these studies. Dosimetry was performed using small thermoluminescent dosimeters (TLDs) placed on the surface of the 2-cm long angioplasty balloons, inflated with contrast medium to a diameter of 2.5, 3, 3.5, and 4 mm. Radioactive 90Y wires were left in teh inner balloon catheter and the surface dose rate was measured and extrapolated to 72 h after activation to allow a comparison between the values obtained. After observing the poor centering of the source within the standard angioplasty balloon, a new centering balloon was developed. A conventional balloon was subdifived into four evenly spaced interconnecting chambers, thus assuring adequate centering of the inner catheter. Thermoluminescent dosimetric measurements were performed with a 3.5 mm centering balloon to evaluate the homogeneity of the surface doses compared to those measured with the conventional balloon. Results : Thermoluminescent dosimetric measurements using the standard balloons filled with contrast medium were plotted semilogarithmically as a function of distance from balloon surface. The logarithms ofthe measured doses fit a straight line as a function of depth. The doses at 1 mm and 3 mm are approximately 50 and 10% of teh surface dose, respectively. Due to the poor centering of the source in the conventional balloons, the dispersion and standard deviations (SDs) of the measured surface doses increased proportionally to the balloon diameter (SDs are 1.89, 5.52, 5.79 and 6.46 Gy for 2.5, 3, 3.5, and 4 mm balloon dimeters, respectively). Forthe 3.5 mm centering and conventional balloons the respective mean, minimum, and maximum surface doses were 8.41 Gy (min. 7.26; max. 9.46) and 7.89 Gy (min. 2.18; max. 16.06) and their standard deviations were 0.66 and 5.79 Gy, respectively. Conclusions : Conventional angioplasty balloons cannot ensure a homogneous dose delivery to an arterial wall with an intralumental 90Y beta source. Preliminary dosimetric results using a modified centering balloon show that it permits improved surface dose distribution (axial and circumferential homogeneity), making it suitable for clinical applications.