The method of iteratively reweighted least squares for the regression analysis of Poisson distributed chromosome aberration data is reviewed in the context of other fit procedures used in the cytogenetic literature. As an application of the resulting regression curves methods for calculating confidence intervals on dose from aberration yield are described and compared, and, for the linear quadratic model lambda = beta 0 + beta 1 chi + beta 2 chi 2 a confidence interval for the ratio beta 1/ beta 2 is given. Emphasis is placed on the rationale, interpretation and the limitations of various methods from a statistical point of view.