The recently developed method of etching fission fragment tracks in mica appears to be applicable to the measurement of neutron exposures in irradiation tests. The sensitivity of the method depends on the concentration of fissile elements. The naturally occurring uranium which is present in trace quantity can be used to measure thermal neutron exposures of 1016to 1021neutrons/cm2. Deposition of fissionable material on the mica would increase the sensitivity to permit measurement of 106to 1011neutrons/cm2. Density counts are reproducible to approximately 5% by using simple laboratory techniques.