Current experience using the laboratory rat in aging studies.

: The breeding and maintenance conditions for 2 strains of inbred rats, the WAG/Rij and BN/Bi rats, were described. The survival characteristics of these 2 strains were compared with those of 2 other experiments in which rats were kept for longevity studies under different environmental conditions of microbiologic status and diet. Data were provided on the rate and types of spontaneous tumors found in these 2 rat strains. It can be concluded that in order to obtain rats of good quality and in sufficient numbers for aging studies, breeding and raising the animals under strict SPF conditions is warranted. It is also necessary to maintain them under "clean conventional" conditions for long-term studies.