AbstractThe incidence of reinfection with rubella among conscripts of the Finnish Defence Forces was studied by serological methods. Paired sera were collected from 403 recruits of a garrison at the beginning and at the end of the service period (8 months). Additional sera from 367 of these men were obtained at the middle of the service period. The specimens were investigated by haemagglutination inhibition (HI), and possible infections and reinfections were further confirmed by neutralization (NT) and complement fixation (CF). 28 conscripts (7%), lacking HI or NT antibodies in the initial serum samples, contracted rubella; only 7 developed a clinical disease. Thus, the ratio of subclinical to clinical infections was 3 : 1. Judged from the HI test, done with kaolin-absorbed sera, 21 of 393 conscripts (5.3%) might have had a reinfection. The NT test indicated, however, that the majority of the low HI titres in the initial sera were non-specific. Possible serological evidence of subclinical reinfections rem...