Dermatophilosis is one of the most important diseases of domestic ruminants in the Caribbean islands where the clinical disease has been shown to be associated with the presence of the tick Amblyomma variegatum. Seroepidemiological studies were conducted to clarify the epidemiology of the disease in the region with a particular attention paid to the role of A. variegatum. A bank of 1300 cattle sera from the Lesser Antilles was screened by ELISA for the presence of antibodies to Dermatophilus congolensis. It appeared that seropositive animals do exist in islands non infested by A. variegatum and where dermatophilosis is never or seldom seen. Moreover, there was no significant difference in prevalence of seropositive animals between tick-infested and non infested areas of Martinique and Saint Lucia, 2 islands partly infested by the tick, and where dermatophilosis is only seen in tick-infested areas. Prevalence was low in small islands with a dry climate. This confirms experimental data showing that A. variegatum is not necessary for the transmission of D. congolensis which is widespread in most of the islands. High concentrations of prostaglandin E2 (between 151 and 377 ng/ml) and prostacyclin (between 124 and 134 ng/ml) found in the saliva of females A. variegatum strongly suggest that the tick could favour the development of the lesions through an immunomodulating activity of its saliva. However, despite some success in reproducing dermatophilosis on goats simultaneously infested with adult A. variegatum and scarified with Dermatophilus, no difference was observed between naturally resistant Creole cattle and very susceptible Brahman animals using the same model. The lesions of dermatophilosis remained very mild on animals of both breeds.(ABSTRACT TRUNCATED AT 250 WORDS)