Clinical, histopathological and immunohistochemical findings are presented from a series of cutaneous lymphoid neoplasms including canine epitheliotrophic lymphoma (n=7), canine non-epitheliotrophic cutaneous lymphoma (n=10), canine cutaneous plasmacytoma (n=10) and feline non-epitheliotrophic cutaneous lymphoma (n=6). Three cases of canine epitheliotrophic lymphoma expressed the CD3 T-lymphocyte marker, but the remainder were negative for this molecule and for a panel of B-cell markers. Non-epitheliotrophic cutaneous lymphoma was shown to be predominantly of T-cell phenotype (CD3 + ) in the dog (eight of 10 cases) and cat (five of six cases), the remaining cases in both species being of B-cell origin, expressing the γ heavy chain of immunoglobulin (with or without λ light chain). One canine non-epitheliotrophic B-cell lymphoma expressed IgG of the IgG2 subclass. Two of the biopsies from dogs with cutaneous plasmacytoma were shown to express immunoglobulin α chain (one with λ chain) and two neoplasms were positive for immunoglobulin γ chain (both with λ chain). One of the latter immunoglobulins was of the IgG4 subclass. In the majority of all cases of cutaneous lymphoid neoplasia examined, there was a local polyclonal immune response, manifested as infiltration by a mixed population of plasma cells expressing IgG (IgG2, IgG4), IgA or IgM. In the feline tumours CD3 + small T lymphocytes were included in these infiltrates.