Models are proposed to extend the monthly streamflow data at a site where the available historic rainfall and streamflow data are too short for adequate systems study, subject to the condition that there are no gauging sites in the basin or adjacent basins with a longer period of streamflow data. Hence rainfall data of a nearby raingauge station are used. Five regression models, namely, runoff coefficient model, single linear regression, monthly linear regression, monthly linear regression with stochastic description for residuals, and a double regressed model are used. The results show that the monthly linear regression model with stochastic description for the residuals is best suited for the purpose when applied to a case study. © 1995 Taylor and Francis Group, LLC.