Most change-point models assume that the response is continuous or cross sectional binary.However,in many public health problems,the data is longitudinal binary.There are few studies of change-point problems for longitudinal outcomes.This paper describes a flexible change-point model which includes random-effects and takes into account the difference between various individuals in longitudinal binary data.A transition function is used to make the linear-linear logistic model differentiable at the change-point.The location of the change-point is estimated using the maximum likelihood method.Adjust-ment of the transition parameter from zero to one controls the sharpness of the transition.The performance of this estimation procedure is illustrated with simulations using SAS/proc nlmixed and a detailed analysis of data relating hormone levels and ovary functions based on data from the Obstetrics and Gynecology Hospi-tal,Medical Center of Fudan University.