Background: Esters of phthalic acid are widely used as plasticizers for many types of plastics ranging from polyvinyl chloride to food wraps, toys and building products. Exposure to phthalates is universal. Recent studies have documented subtle evidence of phthalate toxicity. The principal route of exposure is believed to be dietary - through ingestion of food products via contaminated packaging. Other routes include outgassing. Astronauts necessarily eat food pre-packaged in plastics. The objectives of this study were to determine whether phthalate levels increased during long duration space flight on MIR. Methods: Urine was collected from 6 astronauts and cosmonauts before, during and after space flight. To avoid confounding the results with phthalates derived from plastic containers used for sample collection the urines were analyzed for a metabolite of the major environmental phthalate ester, Bi(2-ethylhexyl) phthalate (metabolite monoethyl phthalate, MEP) by isotope dilution-gc-ms. Results: MEP excretion was increased by 235 + 33.