  This paper discusses the possible ways to analyse the data, adopting a matrix
notation, so often used in Bioassays. The paper also reviews the Multistage
Models (MM). The MM class of models is applied for extrapolation, to the region
of Low-Dose. The effect of covariates in experimental carcinogenesis is
introduced and the relative efficiency is evaluated. Certainly the discussed
case was refereed to uncorrelated covariates and therefore an open problem
might be the multicollinear predictive covariates.Various nonlinear models are
discussed, giving more emphasis on the Michaelis-Menten and the Fisher's
information for them is discussed
