An equation based on enzyme kinetics was used to describe the effects of temperature on poikilothermic activity rates. This equation successfully described change in activity rates for both a variety of poikilotherms and rates including: photosynthetic, O2consumption, glucose oxidation, handling, search, and generation rates. All of the data sets tested had r2values greater than 0.92. This equation was the major component of a model predicting the interaction of temperature and a limiting nutrient on an activity rate. The model was developed from the case, where Kmis considered to be the product of two temperature dependent rates and allowed Kmis to be a simple or complex function of temperature. The model successfully described the interaction of temperature and limiting nutrient on rates from two data sets.