Systematic hand-held radiometer measurements of lava surface temperatures in active flows and tubes on Kilauea volcano, Hawai'i reveal complexities that cannot be resolved in remotely sensed data from aircraft or satellites. Using portable infrared Minolta/Land Cyclops radiometers, we measured surface temperatures of flows at various distances from their sources and investigated cooling rates and the development of crust. Our measurements suggest that the upper surface of these lava flows can be split into a minimum of four thermal components: core (>1050°C), visco-elastic skin (750-900°C), rigid solid crust (<750°C), and flow margins (<175°C). For the 'a'a flows investigated, a cool rigid crust characteristically developed in the central part of channels within 30 m of the source vent and incandescent lava was exposed in the marginal shear zones of channels. This affects the heat loss and morphology of lava in active channels. Our investigations of temperature distributions on pahoehoe flow fields reveal temperature anomalies of up to 150°C above active tubes and tumuli.