Summary A portable clinical centrifuge has been modified so that it can be used as a continuous-flow centrifuge. An adapter fitted to the head of the instrument delivers the test liquid through four flexible tubes inserted into centrifuge shields used as collecting vessels. The waste liquid overflows the vessels and is discharged through a drain in the centrifuge bowl. Cercariae of Schistosoma mansoni were successfully recovered alive from 1 to 20 liters of water. The centrifuge is suitable for field studies and, since a large proportion of the cercariae was recovered from test runs, the instrument may be useful for study of natural cercaria populations. The centrifuge may also be useful for concentration of other microorganisms from water and so may be of value to oceanographers and limnologists.