A photographic version of the Mallampati test was developed and applied to 242 pregnant patients at 12 weeks' gestation and again at 38 weeks' gestation. At 38 weeks the number of grade 4 cases had increased by 34% (P < 0.001). This is in agreement with other evidence which suggests that difficult laryngoscopy is slightly more frequent in obstetrics (1.7%) than in general surgery (1.3%). The increase in Mallampati score correlated with gain in body weight (r = 0.3, P < 0.001), which gives some support to the concept that fluid retention is the underlying cause. We conclude that pharyngeal oedema causes some hindrance to tracheal intubation in obstetrics, but not enough to explain the high failure rate reported. A case is made for rationalizing the management of difficult intubation. Our data also show that more research is needed on factors which affect Mallampati's test, particularly neck extension.