Concentrations of total serum IgE, IgA, and IgG were measured in 36 atopic and 16 parasitized dogs, and compared them with 30 healthy control dogs. IgE was measured using enzyme-linked immunosorbent assay. IgA and IgG were measured using radial immunodiffusion assays. Mean total serum immunoglobulin (Ig) E concentrations in healthy, atopic and parasitized dogs were 7.1 units (U) ml-1, 5.8 U ml-1 and 14.3 U ml-1, respectively. Mean total serum IgA concentrations in the same groups were 103.3 mg dl-1, 63.2 mg dl-1 and 67.3 mg dl-1, respectively. Mean total serum IgG concentrations were 1066 mg dl-1, 1621 mg dl-1 and 1480 mg dl-1 in the three groups. There was no significant difference in IgE concentrations between these groups of dogs. IgA levels were significantly lower in atopic and parasitized dogs compared with healthy dogs (P < or = 0.05), whereas IgG levels were significantly higher in the atopic and parasitized dogs (P < or = 0.005). These results suggest that measurement of total serum IgE would be of no benefit in the preliminary clinical investigation of a suspected atopic dog. The lower IgA and higher IgG concentrations in both atopic and parasitized dogs suggest that similar regulatory mechanisms governing immunoglobulin synthesis occur in canine allergic and parasitic disease, promoting IgG synthesis but down-regulating IgA production.