Sperm chemotaxis is an area of significant interest to scientists involved in reproductive science. Understanding how and when sperm cells are attracted to the egg could have profound effects on reproduction and contraception. In an effort to systematically study this problem, we have fabricated and evaluated a microfluidic device to measure sperm chemotaxis. The device was designed with a flow-through configuration using a spatially and temporally stable chemical gradient. Mouse sperm cells were introduced into the chemotaxis chamber between confluent flows of mouse ovary extract and buffer. The sperm experiencing chemotaxis swam toward the extract and were counted relative to those that swam toward the buffer. The ovary extracts were diluted from 10(2) to 10(7) times, and each extract dilution was screened for chemotaxis. Four out of six ovaries showed a strong chemotactic response at extract dilutions of 10(-3) to 10(-5). This device provided a convenient, disposable platform on which to conduct chemotaxis assays, and the flow-through design overcomes difficulties associated with distinguishing chemotaxis from trapping.