Objective: To investigate gustatory and olfactory sensitivity in the first trimester of pregnancy using validated test kits. Design: Prospective study. Setting: Department of Obstetrics, University Hospital Zurich, Switzerland. Population: Total 53 pregnant women and 59 controls in a known phase of the menstrual cycle. Method: Gustatory sensitivity was assessed by requiring subjects to discriminate between four basic-taste tablets ('sweet', 'salty', 'sour', and 'bitter'). Olfactory testing was performed using the 'Sniffin' sticks' kit. Subjects rated the intensity and hedonic tone of the four tastants and of 10 common odors. Results: Pregnant women had significantly lower overall gustatory sensitivity scores. There were no differences in olfactory sensitivity. However, pregnant women rated the odors 'rum', 'cigarette' and 'coffee' as more aversive than did non-pregnant women. Conclusion: Our data do not support the hypothesis of a generalized increase in chemosensitivity in early pregnancy. In terms of adaptive changes of the olfactory system may act as a sentinel to potentially harmful chemicals. In contrast, the gustatory system appears to retreat to allow a greater intake of electrolytes and a more widely sourced diet. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.