Genetic monitoring is an essential component of colony management and for the rat has been accomplished primarily by using immunological and biochemical markers. Here, we report that simple sequence length polymorphisms (SSLPs) are a faster and more economical way of monitoring inbred strains of rats. We characterized 61 inbred strains of rats, using primer pairs for 37 SSLPs. Each of these loci appeared to be highly polymorphic, with the number of alleles per locus ranging between 3 and 14 and, as a result, all the 61 inbred strains tested in this study could be provided with a unique strain profile. These strain profiles are also used for estimating the degree of similarity between strains. This information may provide the rationale in selecting strains for genetic crosses or for other specific purposes.