The lengths of 25 male and 25 female worms from each of 4 rats with worm burdens ranging from 190 to 361 were compared with similar measurements from 4 rats that harbored from 1710 to 2290 worms. No difference was found between the lengths of the worms from these light and heavy infections, and it was concluded that a crowding effect pheno-menon does not exist in N. brasiliensis infections of laboratory rats. The authors suggest that this may be correlated with the belief that the adults of N. brasiliensis are tissue feeders.