This report describes a dot enzyme-linked immunosorbent assay (Dot-ELISA) for detecting circulating antigens in the sera of dogs infected with Dirofilaria immitis (D. immitis). Circulating D. immitis antigens could be detected in 24 of 25 infected dogs. The remaining animal had two immature worms. However, non-infected dogs and dogs infected with other parasites were all negative. Few cross-reactions to different parasite antigens were observed. The advantages of the Dot-ELISA include; 1) there is no need for pretreatment and dilution of sera and samples could be immediately bound to nitrocellulose paper set into microfiltration apparatus, 2) this assay could be carried out within 2 h at room temperature, 3) the resulting enzyme-reaction could be measured by both visual observation and densitometric reading.