Ciliate samples were collected from Lake Fryxell by drilling a hole through the thick ice cover (approximately 4m thick) above the deepest point of the lake. A 2.21 Niskin bottle was used to retrieve duplicate 500 ml water samples from a 9m depth. The water samples were fixed in Lugol's iodine and concentrated by settling, prior to counting in a Sedgewick-Rafter counting chamber under phase microscopy at x160. Cryptophyte biomass was calculated by measuring 50 cells on each preparation. Biovolume was derived by applying an ellipsoid geometric shape and converted to carbon using a conversion figure of 220fg C/microm3. Ciliate ingestion rates were determined using live cryptophytes. Ciliates were incubated in the dark at 2 degrees C until no autofluorescence from ingested cryptophytes was visible within the cells. Freshly collected cryptophytes were concentrated by gravity filtration. The ciliates were then incubated with two concentrations of cryptophytes, 8500/ml and 15000/ml. The former concentration is typical of the deep maximum of cryptophytes in Lake Fryxell, the latter is close to the highest level ever recorded in Lake Fryxell. Ingestion rates were measured at 6 intervals over an 8 hour period. Samples were fixed with ice-cold 2% glutaraldehyde (final concentration), filtered onto 10 microm polycarbonate filters and viewed under epifluorescence microscopy. Ingested cryptophytes were visible within the ciliates by their orange autofluorescence. Fifty ciliates were examined on each preparation.