Polyacrylamide gel electrophoresis and subsequent esterase staining provide an alternative to immunological methods for investigating the diet of microarthropods which cannot be observed directly. Attack rates in field populations of Antarctic microarthropods by the predator Gamasellus racovitzai were calculated by proportional and quantitative analyses of electrophoresis results. Results were quantified by transmission densitometry and a digestion curve for ingested prey esterases was defined. An exponential decay model of digestion, incorporating meal size, was used, and a method potentially enabling both the time since feeding and the composite meal size to be estimated for individual predators is described. These methods are applied to samples of predatory mites collected from the Antarctic Peninsula. Although estimated attack rates were low, about 0.1–0.3 prey per predator per day, they may be sufficient to cause severe local reduction in prey density.