Three types of materials of special interest to the NIH Biomaterials Program were evaluated for their tendency to induce hemolysis when exposed to a laminar blood flow between rotating parallel disks. The three types were: (1) TDMAC-heparinized surfaces of polycarbonate (Lexan), silicone rubber, and polyvinylchloride; (2) polyacrylamide hydrogels (PAH) prepared by three different chemical processes; and (3) fluorinated ethylcellulose (FEC). All were compared to a polyethylene (PE) standard, to normalize data for variations in blood quality. Multiple tests, showing good reproducibility, demonstrated: FEC is a very low hemolyzer, about 60% of the PE; PAH surfaces are poorer than PE, giving 120-220% of PE hemolysis depending on fabrication and shipment history; and TDMAC-heparinized surfaces are highly hemolytic, in the range 160-440% of PE depending on substrate. Plastics used as substrates for the coating cited above were also evaluated: Delrin, Lexan, Nylon 6, propylene, and a polyether urethane. Tentative explanations are advanced for hemolytic variations, in terms of surface chemistry and material interactions with the blood.