A large block of simple sequence repeat (SSR) polymorphisms for the dog genome has been isolated and characterized. Screening of primary libraries by conventional hybridization methods as well as by screening of enriched marker-selected libraries led to the isolation of a large number of genomic clones that contained (CA)n repeats. The sequences of 101 clones showed that the size and complexity of (CA)n repeats in the dog genome were similar to those reported for these markers in the human genome. Detailed analysis of a representative subset of these markers revealed that most markers were moderately to highly polymorphic, with PIC values exceeding 0.70 for 33% of the markers tested. An association between higher PIC values and markers containing longer (CA)n repeats was observed in these studies, as previously noted for similar markers in the human genome. A list of primer sequences that tag each characterized marker is provided, and a comprehensive system of nomenclature for the dog genome is suggested.