The antigens present in an extract of dog hair and dander were examined by crossed immunoelectrophoresis (CIE) and the IgE-binding allergens by crossed radio-immunoelectrophoresis (CRIE), respectively, using sera from 60 British and Finnish animal-allergic subjects. The extract was comprised of a minimum of 28 antigens, 11 of which were common to dog serum. IgE antibody in the sera of the dog-sensitive patients bound to 21 of the 28 antigens at varying frequencies and intensities. Binding of any intensity occurred most frequently to two serum proteins: antigen 23 (IgG) binding IgE in 88% of cases, and antigen 3 (dog serum albumin, DSA) in 77% of cases. Dander antigen 8 bound in 63% and antigen 1 in 42% of the sera. Strong IgE binding, however, was most commonly associated with dander antigen 8 followed by antigens 1 and 23 (IgG) then 3 (DSA). The ranking of the antigens as allergens was similar for the two populations except that DSA was more important for the British than for the Finnish subjects.