Most immunoassays are based on microtiter plates with conventional polystyrene (PS) as a solid support. PS is produced from crude oil. The production of PS plates consumes several hundred thousands tons of valuable raw material of limited supply. Also, disposing of PS plates by incineration produces a complex mixture of pollutants including dioxins and polycyclic aromatic hydrocarbons (1), and it adds excess CO2 to the atmosphere. In contrast, biopolymers such as polylactic acids (PLAs) are produced from renewable resources; they are biodegradable and their CO2 balance is neutral. PLA-based polymers have successfully replaced synthetic polymers in several applications, including some recent applications in immunology (2)(3). For the development of a PLA formula suitable as a matrix for immunoassays, the physical properties and surface characteristics of the polymer had to be improved for the present study. Surface characteristics are affected by factors such as monomer content, the nature and concentration of various additives, and molding and releasing conditions. Moreover, lot-to-lot reproducibility is affected by industrial fermentation and extraction procedures. For this study, the injection-molding process commonly used for PS was adapted to the PLA polymer to produce an experimental batch of 96-well microtiter plates from suitable PLA formulations. The performance of these plates in an ELISA was compared with conventional commercial PS plates. We used recombinant measles virus hemagglutinin protein (H-ELISA) as antigen for the detection of measles-specific IgG (4)(5)(6). We analyzed a panel of 426 human sera using 96-well prototype microtiter plates made of PLA. The procedure was applied essentially as described (5). All study participants or their parents gave informed consent. Results were compared with those obtained with the same antigen and commercial PS Maxisorp microtiter plates (NUNC). Statistical analysis of data was performed with SigmaStat software (Jandel Scientific). A z …