The ECP Working Group on AIDS has evaluated the available data on seropositivity to HIV-1 supplied by research groups in 12 Eastern and Western European countries. The period covered is 1985 and 1986. A significantly elevated incidence of seropositives was observed in both females and males in heterosexual contact with members of high risk groups. In contrast heterosexuals with no such contact had an incidence below 1%. For male homosexuals from Italy, Denmark and Switzerland the trend was no detectable increase in prevalence from 1985 to 1986. Hungary and Poland now have a few per cent seropositive male homosexuals, but no seropositives were found in a group of Polish drug abusers.