Over a 6-year period seven adult horses of different breeds and genders dev
eloped multifocal, exudative, oozing dermatitis characterized histologicall
y by epidermal spongiotic vesicles and perivascular eosinophilic, neutrophi
lic and mixed mononuclear inflammation. Three horses were pruritic. Systemi
c disease was not noted. Two horses had a history of recurrent urticaria (h
ives) and one horse had nodules or welt-type lesions that progressed to exu
dative, oozing lesions. Interepithelial immunoglobulin (Ig)G was detected b
y avidin-biotin complex-peroxidase staining, but the pattern of staining wa
s more consistent with epithelial oedema than specific IgG deposition assoc
iated with pemphigus. The exudative oozing lesions developed under circumst
ances suggesting that dermal oedema progressed to intracellular and interce
llular epidermal oedema, which in turn progressed to the spongiotic vesicul
ar epidermal lesions.