An adult maleRattus norvegicns,with a greyish‐brown sandy colour, similar to the mutantbrownassociated with the normalagouti’allele, was trapped near Pavia in the year 1958. In 1960 we started a line by crossing this unusual animal with an albino female. After several years (in 1987), the progeny of these crosses produced a female affected by motor disorder corresponding to the description of the mutantwaltzer.The close correspondence of the observed phenotypes withbrownandwaltzersuggest alle‐lism between the mutants responsible; however a direct test to confirm allelism was unfeasible. The origin of the mutants, their observed phenotypic properties and inheritance and, with regard towaltzer,degree of penetrance, are here reported.