It is known that nitrous oxide (N 2 O) inactivates vitamin B 12 and causes hyperhomocysteinemia. The personnel working at the operating theatres are repeatedly exposed to N 2 O in the ambient air. This prompted us to investigate the biochemical indices of vitamin B 12 metabolic status among female personnel working under various levels of N 2 O exposure. In this study, the homocysteine and folic acid levels were assessed and bad obstetric outcome was questioned. Sixty operating theatre female personnel were examined. Vitamin B 12 and folic acid, total homocysteine level, anticardiolipin IgM, IgG, antiphospholipid IgM, IgG levels were measured in serum. A questionnaire inquiring about obstetric history was given. The serum concentration of folic acid was 10 ± 3.3 nmol liter -1 . The vitamin B 12 level was 332 ± 134 pmol liter -1 , the serum concentration of homocysteine was 9.1 ± 2.4 nmol liter -1 and all were within normal ranges. There was no difference regarding homocysteine, folic acid, vitamin B 12 levels and the obstetric history between the subjects who had abortus history and the subjects who had not abortus history. Exposure to N 2 O in healthcare workers was not associated with alterations of homocysteine, folic acid status and bad obstetric outcome (Tab. 4, Ref. 18). Text in PDF www.elis.sk.