One central problem in understanding the Martian upper atmosphere is the poor correlation between exospheric temperatures and the energy input from the Sun in the EUV and UV. Turbulence heats the atmosphere by dissipation of turbulent energy and cools it by downward heat transport. A time-variable turbulence may introduce a stochastic component in addition to the solar-driven, regular variation of the exospheric temperatures. To investigate the possible range of temperatures on the basis of this assumption, we developed a one-dimensional mean-dayside model of the energy balance of the Martian upper atmosphere. With plausible assumptions on the range of the eddy diffusion coefficient, we find a stochastic component of ¿63 K for the exospheric temperatures. The comparison of observed data with the results of our model yields a best value for the efficiency of the heating by absorption of solar ultraviolet radiation 0.145¿0.05. ¿ American Geophysical Union 1987