The design of a microperfusion chamber is presented for use with spermatozoa or other cell suspensions. This chamber allows perfusion of a small number of spermatozoa during simultaneous observation of cell behavior at the microscope. The chamber is made from a flat glass capillary tube that is fitted at both ends with a filter unit containing Millipore filter discs. The entire assembly is designed to fit the stage of an inverted microscope. A population containing as few as several hundred sperm cells may be observed in the chamber during successive changes of the suspending medium as controlled by a perfusion pump. Several experiments are presented demonstrating sperm survival in the sealed chamber and the response of rabbit and human sperm motility after the washing process. For these manipulations, the percentage of motile cells, linear swimming speed and incidence of hyperactivated motility are reported. Simple incubation in the chamber for 1 hour was not deleterious to the motility of rabbit spermatozoa. Human seminal spermatozoa showed no decline in vigorous motility after the washing procedure. Compared with in vitro capacitated spermatozoa, however, washing of rabbit seminal spermatozoa showed a variable response. Finally, partially capacitated human spermatozoa were examined for any alteration of motility during chamber incubation with a subsequent wash. When small numbers of spermatozoa or other cell types must be manipulated, the methodology can be effectively substituted for the standard washing procedure that uses repeated centrifugation and resuspension.