Human lens epithelial (HLE) cells were explanted into medium containing different concentrations of foetal calf serum (FCS) and serum substitute. The proliferation of cells was measured as a function of time in culture and the growth parameters (growth rate and proliferative capacity) were determined by the application of the Gompertz growth function. Human lens epithelial cells have a limited growth capacity in culture of five to seven population doublings and this decreases with age. The population doubling level (PDL) was determined empirically and from fits of the Gompertz equation. The values of the PDL determined experimentally and theoretically are compared for a series of different culture conditions. Exposure of the cells to raised levels of FCS caused a reduction in proliferative capacity; the PDL decreased from 6.3 to 5.5 when the serum was raised to 50% although the growth rate increased. Serum substitute caused a decrease in the growth rate without changing the proliferative capacity and also altered the cellular morphology. It is hoped that the method described will have applications to the study of posterior capsule opacification following extracapsular cataract extraction and phacoemulsification and will aid in the development of preventive therapies.