An attempt is made at finding general mathematical expressions for intensity characteristics of sensory receptors. Analysis of responses of an auditory nerve unit and of a Pacinian corpuscle lead to the derivation of two simple equations that describe the relationships between the stimulus energy, or a variable proportional to it, and either the average receptor potential or the average firing rate of receptor units. The transformation between the two equations reflects the relationship between the two response stages. The equations imply that the receptors first linearly integrate an energy-proportional variable, then perform a power-function transformation on the result. An exponential function is derived for the response saturation at sufficiently high stimulus levels. The equations generate numerical values in close agreement with empirical intensity characteristics of auditory and other mechanoreceptors, of photoreceptors, and of chemoreceptors. Usually, a power of approximately 0.5 is followed, but gustatory receptors appear to obey a power of 1.0.