New strains of ODU plaque-susceptible and resistant rats have been developed starting from litter mating at our laboratory, in 1972. Those strains were selected and mated for further generations. ODU plaque-susceptible and resistant rats are those that show the presence or absence of plaque formation in their gingiva of lower incisors after they are fed a commercially available powder diet. Experiments were started when rats weighing 75 to 85 gm were about 5 weeks old being fed with 20 gm of a powder diet a day. Almost every 4 days, plaque formation was observed in terms of 5 degrees from zero to 4 degrees and body weight. As a result, plaque formation in plaque-susceptible and resistant rats clearly showed their quality in their 3rd generation. Those qualities will be further emphasized as the generation advances. In the 3rd generation of plaque-susceptible rats, no difference was found in growth between those ingested with a powder diet and those with a solid diet of the same ingredients. But in the first 2 months, male plaque-resistant rats of the 3rd generation grew more quickly than susceptible rats.