In the laboratory, specimens of the marine sponge Halichondria paniaea Pallas (1766) were fed' with various defined particles for 2-h periods. Excretion products were collected and inspected by microscopy. The results show that H. panicea is able to pack singly ingested particles into spherical aggregates held together by a thin cover. Concerning partiele number and density, the composition of these faecal pellets depended on the feeding condition of the sponge and the quality of the food. Sponges in good feeding condition egested more and bigger faecal pellets than those previously starved. Digestible and indigestible particles were excreted by the sponge in different ways. Indigestible particles passed through the sponge more rapidly and were also egested as single particles without cover. In contrast, digestible algae were always egested as faecal pellets.