ANTRINTM photosensitizer, a lutetium texaphyrin-containing drug, is currently being evaluated in the clinic as a phototherapeutic agent for the treatment of peripheral vascular disease using photodynamic therapy, a procedure which has been designated as photoangioplasty. In order to better understand light delivery/timing, disease indication, and the features necessary in the design of light delivery devices, studies were carried out to measure the effect of hematocrit and photosensitizer concentration on the transmission of 732 nm light in rabbit blood and plasma. In blood, light transmission decreased exponentially with increasing hematocrit. An increase of 10 in the hematocrit (e.g., 35 to 45) resulted in a 40% decrease in the amount of transmitted light. In plasma, high concentrations of AntrinTM were observed 3 and 5 hours post administration (31.8 plus or minus 9.3 (mu) M and 14.3 plus or minus 8.3 (mu) M, respectively) compared to 24 hours after administration of the sensitizer (2.5 plus or minus 1.4 (mu) M). Increased plasma sensitizer levels correlated with decreased light transmission through plasma due to absorption of light by lutetium texaphyrin. An increase in the delivered light fluence would therefore be expected upon irradiation 24 hours versus 3 or 5 hours post administration of AntrinTM. However, other factors, such as drug uptake by plaque, would need to be considered in order to optimize the time interval between injection and irradiation.