Three strains of laboratory rats (Wu:Cpb, CPB-B and WKY/Cpb) differing widely in reproductive success were compared concerning the role played by maternal behavior in the survival probability of pups. Parturition behavior of the dams was selected for study as pups are most dependent on the mother's behavior at, and immediately after birth. Great strain differences in survival rate of life born pups were found. However, differences between strains in parturition behavior were found to be restricted to only one pup oriented behavior and some non social behaviors. Besides no pups died at the day of birth nor did it seem probable that the strain differences we found in parturition behavior can be held responsible for the eventual death of pups during parturition. The suggestion is presented that strain differences in maternal behavior which affect survival chances of pups are to be looked for in the lactation period.