Absolute volume estimates of total material ingested by ephemeropteran nymphs of various sizes (34 sites including 20 species) were made using an electronic counter. Based on 12 months data, detritus accounted for 90% of the stomach contents by volume, and the remaining 10% of the food material consisted almost entirely of diatoms. The relationship between absolute total volume of stomach contents and total length of nymphs fitted an exponential function. Nymphs of the smallest (2–4 mm) and largest (14–16 mm, 16–18 mm) size classes tended to have a smaller volume of ingested material than would be predicted by the regression.