[en] BACKGROUND: Body weight loss occurring after a hypoenergetic diet or a gastroplasty could be followed by an increase in blood concentration of potentially toxic pollutants that can interfere with the hormonal system (endocrine disrupters). DESIGN: Thirty obese individuals recruited for gastroplasty were compared before and after treatment with 45 normal-weight people. MEASUREMENTS: Blood samples were analyzed for DDT, DDE, HCB and PCBs no. 28, 52, 101, 118, 138, 153 and 180, by gas chromatography-mass spectrometry. RESULTS: The results indicate clearly that body weight loss occurring after gastroplasty increases plasma concentration of lipophilic pollutants. CONCLUSION: Gastroplasty increases plasma concentration of organochlorine pesticides and PCBs, which could be a risk factor of endocrine disruption. Future longitudinal research will have to determine if the advantages of body weight loss are reduced by this potentially harmful effect.