This paper considers nonparametric estimation of lifetime distribution based on grouped data from constant stress accelerated life tests under intermittent inspection in which test items are inspected only at specified points in time. A method of estimating the lifetime distribution at use condition stress is proposed for the case where the time transformation function relating stress to lifetime is a version of inverse power law. Numerical studies show that the proposed method is comparable to the maximum likelihood method for small sample size and is more accurate than existing nonparametric methods used for continuous inspection. The method performs better than the maximum likelihood method when the underlying lifetime distribution is incorrectly specified. (C) 1996 Elsevier Science Limited.