The male accessory glands of Glossina austeni Newst. contain an apical secretion—a dense, opaque, whitish secretion at the apical end of the gland, and a diffuse secretion—a bulkier, more mobile, translucent, whitish secretion occupying nearly all the remainder of the gland. There is also a plug of clear solidified accessory material preventing the outflow of secretions from the resting gland. By immersing the whole accessory gland in a saline medium at pH 2·2, and then transferring the specimen to distilled water, the apical secretion can be separated manually from the rest of the gland, as an apical body. Measurements of the apical body in virgin male flies show that the apical body increases in width according to the equation: Age ≐ constant Χ width 2.5, but individual deviations from this relation were considerable. Immediately after mating the apical body is long and thin; recovery to approximately the resting condition is complete after 48 h, but, on average, mated males have thinner apical bodies than virgin males of the same age. The use of apical secretion measurements to assess mating frequency under field conditions might be possible if adequate samples of males were available.