We report measurements of the temporal fluctuations of the heat-flux in Ray
leigh-Benard turbulent convection, Although being a global quantity, i. e.
spatially averaged on the flow field, we show that its probability density
function (PDF) is non-gaussian and asymmetric. The ratio of the rms fluctua
tions of the heat flux to their mean display a power law. Ra-gamma with gam
ma = 0.25, on more than two decades in Rayleigh number (2 10(7) < Ra < 4 10
(9)), Thus, the fluctuations are roughly proportional to the temperature di
fference. We discuss this law and we propose a simple mechanism to explain
the non-gaussian character of the PDF.