The broken topography of mountainous regions creates a complex mosaic of topoclimates. Spatial analyses of many climatic elements on a horizontal planar projection of such topography are almost meaningless. Therefore, in this study of potential evapo- transpiration (PET) in Nepal, the vertical dimension (elevation) was chosen as the basis for spatial analysis. A form of the Penman method is used to estimate monthly PET for 11 stations, and an empirical method, developed from Penman values, is used for 13 additional stations. The PET values for each month regressed against elevation (which ranged from 100 to 3,700 m) give quite con- sistent, good correlations (r2 ranging from 0.61 to 0.89). The seasonal variation of PET and its elevational gradient is systematic and consistent with the seasonal and elevational patterns of related climate parameters. The resulting equations permit interpolation and hence integration over the vertical dimension of a cropping region or watershed, facilitating the application of PET data to irrigation timing, stream-flow estimation, crop condition monitoring, and agro-climatic classification in the mountainous terrain of Nepal.