The hydrology of a small wet forested region is studied. Catchment discharge, solar radiation, air temperature, humidity, precipitation, soil moisture, and the water elevation in a swamp were monitored for several months in 1973 and 1975. These data are used to investigate various aspects of the catchment's hydrology and in particular to study the catchment's evapotranspirational requirements. The actual evapotranspiration loss is calculated from a water budget approach. The Priestley-Taylor model is used to predict the medium to long-term evapotranspiration from the basin. The predictions based on the model are in very good agreement with the actual evapotranspirational demand. Evapotranspiration is found to play a significant role in the catchment's water balance. KEY WORDS Forest hydrology Evapotranspiration Water balance Priestley-Taylor equation LIST OF SYMBOLS Catchment area (ha) Specific heat of air at constant pressure (J kg-' OK-') Catchment discharge rate (m3 hr-') Cumulative catchment discharge (m3) Actual evapotranspiration rate (m3 m-' hr-') Cumulative actual evapotranspiration volume (m3) Potential rate of evapotranspiration (m3 m-2 hr-') Equilibrium evapotranspiration rate (m3 m-' hr-') Cumulative equilibrium evapotranspiration rate (m3) Soil heat flux (W m-2) Swamp water elevation (m) Cumulative precipitation (m3) Aerodynamic resistance (m-' hr) Stomata1 resistance (in-' hr) Net solar radiation (W m-2) Adjusted cumulative net radiation (J m-2) Cumulative catchment moisture storage (m3) Time (hr) Air temperature ("C) Elevation of water in weir (cm) Priestley and Taylor coefficient