Consider a feedback amplifierFwith a nonlinear output deviceT_0and an open-loop amplifier A having the same gain and the same output deviceT_0. If the gains of the forward amplifieruand feedback network\betaare independent of frequency, it is well known that under the usual conditions the nonlinear distortion\zetaofFdue toT_0is related to the nonlinear distortion\hat{\zeta}ofAby\zeta = \hat{\zeta}/(1 + u \beta). In this paper conditions are determined under which a similar formula, namely\zeta = (1 + u \beta)^{-1 \ast}, applies whenuand\betaare strictly stable linear time-invariant amplifiers. The interpretation of the formula is the following:\zetais the function of time which is output of an amplifier whose gain is1/(1 + u \beta)when\hat{\zeta}is its input, and\hat{\zeta}is the nonlinear distortion of the open-loop amplifier A.