Five permanent cell lines derived from human gliomas were examined at 24-hour intervals to determine optimal phases of their population growth curves for comparative morphologic studies. In early exponential growth phase, individual cytologic criteria were well displayed, while the increased cellular density of late exponential and plateau phase growth was advantageous for evaluating growth pattern, bizarre multinucleate giant cells and abnormal mitoses. These morphologic characteristics of permanent cell lines derived from human gliomas are potentially useful for correlation with their biologic, immunologic, biochemical and cell biologic parameters.