Three studies were performed to evaluate the breeding ratio of fast breeders containing thorium. In a study of a small breeder, thorium metal and thorium oxide core designs were found to have similar breeding ratios. The slight advantage exhibited by the metal design was not considered significant, since the design was based on a limited amount of thorium metal swelling data. In a study of a 1200-MW(electric) plant, a plutonium-uranium oxide design was compared to a uranium-thorium metal design. The uranium-thorium design had a lower breeding ratio but also had a negative sodium void effect. In the third study, the effect of replacing thorium oxide radial blankets with thorium metal radial blankets was evaluated. This was found to have little effect on the breeding ratio.