A quantitative literature review has been used as the basis of an empirical simulation model of the responses in food intake and egg output of laying hens to temperature, light pattern, light intensity, feeding system type, crude protein, methionine, lysine and metabolisable energy. The financial consequences are considered, by the calculation of gross margin of egg value minus food cost. Response to protein intake in an optimal environment is taken as the first limiting factor. Depressions below the maximum are calculated for sub-optimal environments. The model was tested against a sample of flocks for which detailed records were available, and found to give realistic answers. A FORTRAN program was written which calculates egg output and food intake by 4-week production periods, permitting the user to examine the effects of management changes made during lay. Shortened versions of the model, based on annual values have been written for a programmable calculator.