The author presents the results of a survey for respiratory syncytial virus and adenovirus complement fixing antibodies and parainfluenza viruses 1, 2, 3 haemagglutination inhibition antibodies in a group of 972 chidren between 3 months and 14 years of age. The filter paper method of collecting whole blood was used. Altogether, the percentage of children with complement fixing antibodies against respiratory syncytial virus and adenovirus were respectively 34.6% and 47.7%; 46.8%, 54.1% and 66.6% possessed haemagglutination inhibition antibodies against parainfluenza vírus types 1, 2 and 3. A study on the distribution of the antibodies according to different age groups was also conducted. The present study was undertaken, in order, to examine the distribution of antibodies according to sex and home localization. The following results were obtained: 32.3% of the boys possessed antibodies against respiratory syncytial virus, 49.2% against adenovirus and 60.1%, 65.5% and 78.3% against parainfluenza viruses 1, 2,3 respectively; percentages in girls were 37.4%, 45.9%, 31.1'%, 41.2% and 52.9% respectively. In the rural area 44.8% of the children possessed antibodies against respiratory syncytial vírus, 70.1% against adenovirus, 43.8% against parainfluenza vírus type 1 and 46.8% and 65.4% against parainfluenza viruses 2, 3; in the urban area the percentages observed were, respectively, 30.5%, 38.7%, 47.9%, 57.1% and 67.1%.