In certain toxicological experiments with laboratory animals, the outcome of interest is the occurrence of dead or malformed fetuses in a litter. Previous investigations have shown that the simple 1-parameter binomial and Poisson models generally provide poor fits to this type of binary data. A type of correlated binomial model is proposed for use in this situation. The model is described in detail and is compared to a beta-binomial model proposed by Williams. These 2-parameter models are then contrasted for goodness of fit to some real-life data. Numerical examples are given in which likelihood ratio tests based on these models are employed to assess the significance of treatment-control differences.