When teaching the effect of temperature on biochemical reactions, the problem is usually oversimplified by confining the thermal effect to the catalytic constant, which is identified with the rate constant of the elementary limiting step. Therefore, only positive values for activation energies and values greater than 1 for temperature coefficients ("Q"[subscript 10], defined as the rate change that parallels a 10 [degree]C temperature shift) can be expected. We show why this approach, which is appropriate under saturation conditions, is unsuitable for those enzymes working at subsaturating concentrations of their substrates. To overcome this limitation, we present and discuss a simple thermokinetic treatment of the Michaelis-Menten model for the enzyme-catalyzed reaction. (Contains 1 figure.)