We determined the seroprevalence of a Sindbis-related virus isolated for the first time in 1975 from ticks in south-east Sicily and typed by Gresikova et al. in 1978. An indirect enzyme immunoassay based on viral membrane antigen for coating microtiter strips was used for the detection of immunoglobulin G to the Sindbis-related virus. The method appeared more sensitive than a similar enzyme immunoassay based on crude lysate antigen. Comparison of the results obtained from sera tested both by membrane antigen enzyme immunoassay and microneutralization test showed 92% agreement, while the agreement between microneutralization test and crude antigen enzyme immunoassay was 76%. An overall elevated seroprevalence (63.66%) was found in a population group living in and around the area of first isolation and seroprevalence in different age groups was also studied.