The occurrence of fetal breathing movements was studied in relation to fetal behavioural states 1F and 2F, as recognized by the heart rate patterns A and B, respectively. Simultaneous recordings of fetal heart rate and body, eye and breathing movements were available for analysis (n = 88). These recordings, lasting > or = 2 h, had been made in healthy near-term fetuses during the afternoon or evening, starting about 1 h after the maternal meal. In the majority of recordings fetal breathing activity was lower during heart rate pattern A than during pattern B, but as the opposite occurred in 29/88 recordings (33%), the interstate difference was not significant (P = 0.052). Detailed analysis revealed that breathing movements were more numerous during pattern B than during pattern A if the incidence of breathing during a particular time period was low (30-40% of time). At a high overall breathing incidence (> 40%), however, breathing movements were more often present during pattern A than during pattern B. The latter occurred especially in the first hour of recording, i.e. less distant in time from maternal meals. We conclude that fetal breathing activity is generally higher during state 2F than during state 1F, but a clear-cut state-dependency is absent. Secondly, the relationship between the incidences of breathing during states 1F and 2F depends on the 'drive' or motivation (presumably the blood glucose content) to breathe.