A new model for the prediction of microbial-specific growth rate as a function of temperature is presented. The four parameters of this model are the three cardinal temperatures (Tmax, Tmin and Topt) and the specific growth rate at the optimum temperature (mu opt). A comparison with three other models was made on the basis of several criteria (simplicity and biological significance of parameters, applicability, quality of fit, minimum structural correlations and ease of determination of parameters). A detailed comparison of a 217-point data set, and an extensive comparison of 47 different data sets show that the new model is better than its competitors. The three cardinal temperatures were found to be independent of mu opt. A very strong and unexpected linear correlation between the cardinal temperatures was observed. The consequences of this biological result are discussed, even though causes remain unknown.