When mark-recapture data are analysed by log-linear models, as described by Cormack (1989, Biometrics 45, 395-413), the analysis is in terms of parameters that are related nonlinearly to the parameters of biological interest. For several models formulae are given expressing the variance of the interesting parameter estimates in terms of those provided by a computer log-linear analysis. A device is presented that allows such expressions to be computed simply.