Surface meteorological and surface and subsurface oceanographic data collected during 1979 are used to describe sea-surface temperature, mixed layer depth, zonal current component and net oceanic heat gain fields and to estimate the terms in a heat balance relation for the mixed layer. The terms are evaluated monthly on a 6° of latitude by 10° of longitude grid which covers the equatorial Atlantic from 9S to 9N. The first balance tested is between changes in mixed layer temperature and surface energy fluxes. These fluxes can account for more than 75% of the variance in the original time series of the quadrangles along 6S. Variance reductions are less, along 0° (order of 50%) and 6N (less than 25%). The addition of zonal advection improves some of the predictions but not significantly. Low variance reductions along 6N, west of 20W are attributed to the uncertainties in the estimates of observed temperature change and surface fluxes. The small variance reductions east of 20W, at 6N and along 0° may be related to the neglect of coastal and equatorial upwelling and meridional advection. A simple model is proposed which assumes an annual cycle for the intensity of mixing across the base of the mixed layer, most intense during summer, least intense during winter. Variance reductions at 0°, 5W increase from 20% to 60% with the inclusion of mixing. Meridional advection may also account for a portion of the observed variability in mixed layer temperature.