The daily march of temperature from the surface to 30 km is obtained by combining 6-hourly soundings taken at different times in April–July 1956 and 1958, at a network of eight stations over the Western Tropical Pacific. A mean sounding is derived from this total of 5,227 radiosonde ascents. The daily range decreases from 3.00°C at the surface to a minimum of 0.41°C at 900 mb, then gradually increases upward to values exceeding 1°C near the tropopause and at stratospheric levels. In the surface layer, a single daytime maximum is indicated near 14 LT, whereas double maxima at 12–14 LT and 17–18 LT, respectively, are found from 900 to 650 mb. Downward heat transport by turbulent mixing with the surface layer is suggested from the timing of the temperature maxima and the minimum of the daily range near 900 mb. Nighttime conditions are characterized by a pronounced nocturnal warming in the entire column from 950 mb to the stratosphere. Periodic temperature variations were also calculated from wind variations, using a model based on the linearized equations of motion, frictionless flow, and the assumption that the oscillations are simple progressive waves. However, from the various smoothing procedures applied no reliable derivation of temperature variations from winds can be proposed. Mean lapse rate decreases from the surface layer upward, to a minimum at 850–750 mb, above which it increases to largest values at 350–150 mb. The daily range of lapse rate is conspicuous in the surface layer, but becomes small above 900 mb, except for the stratospheric layers. An attempt is made to assess the daily march of diabatic heat sources/sinks for the tropospheric column as a whole, such as the infrared radiative flux divergenceLW, the absorption of the solar radiationSW, the heating due to condensation of water vaporLP, and the sensible heat flux across the ocean-atmosphere interfaceQ s, obtaining the effect of vertical motion as a residual.LW andQ s vary little throughout the day,SW is a major factor in the daytime heating of the tropospheric column, and the daily march ofLP and the effect of vertical motion are least reliably established. A rainfall maximum and/or subsidence during the hours after midnight are considered as mechanisms for the observed nocturnal warming.