In three of the four subfamilies of higher termites, the anterior hindgut is characterized by an unusually high pH. This phenomenon is especially prominent among the soil (humus) feeders, which represent more than half of all known termite species, but whose digestive physiology is still largely obscure. In this study, we used microelectrodes to determine axial pH profiles in intact guts of the soil-feeding termites Thoracotermes macrothorax, Crenetermes albotarsalis, Noditermes indoensis and two Cubitermes species (all Termitidae: Termitinae). In all species, the pH of the gut contents increased sharply from circumneutral in the midgut to highly alkaline between the midgut-hindgut junction and the first proctodeal dilation (P1). This location coincided exactly with the extent of the mixed segment, a morphologically unique gut region found exclusively among higher termites. The most alkaline pH values occurred in the P1 (pH 11-12.5) and were equal to the highest values ever encountered in biological systems. The second proctodeal dilation (P3) was also alkaline (pH >10), and only in the posterior part of the following segment (P4b) did the gut contents regain a pH close to neutrality. The rectum (P5) was slightly acidic, as was the foregut. Sharp drops of 1-3 pH units were observed between the major gut regions, most notably between P1 and P3, i.e. across the short enteric valve (P2), and also along the P4a. Individual profiles within a species were highly reproducible, as were species-specific differences. The high-resolution profiles presented here show that guts of soil-feeding termites are even more alkaline than reported previously, and they provide sorely needed basic information on microenvironments existing within guts of an extremely important group of terrestrial humivores.