The overall quality of platelets for transfusion is not considered satisfactory by most researchers in the field. The problem is due, in part, to the difficulty of collecting and storing these highly reactive cells, and also to the lack of adequate in vitro methods for assessing quality. We have sought to bring methods of modern cell biology to the investigation of the cellular and biochemical basis of the platelet storage lesion. One approach depends upon the observation that the normal discoid ("plate-like") shape of the platelet changes to a spherical shape during storage. This shape transition is thought to correlate with deterioration of function, so that quantitation of discoid morphology could serve as a measure of satisfactory function. We have developed a device that quantitates the discoid morphology of a population of platelets by measuring the optical properties of the population (Fratantoni, et al, J Lab Clin Med 103: 620, 1984). This measurement is done while the platelets are within a standard container. We are attempting to validate this assay procedure using a rabbit bleeding time system. The rabbit system obviates the problems encountered with human systems and has been well standardized. It utilizes rabbits made thrombocytopenic with cytotoxic drugs and anti- platelet antibody, to compare hemostatic function with optical measurements. Platelets have been subjected to storage at different temperatures, inadequate agitation and volume variation and the optical and bleeding time results compared. Thus far, there has been difficulty in inducing abnormalities that are sufficient to permit comparison between test and control samples. We are now attempting to induce a greater defect by interfering with gas diffusion of the containers-this is done by covering portions of the surface with non-permeable materials. Early experiments have been promising and it is estimated that the project will be completed within one year.