120 children, 71 male and 49 female, aged between 2 years and 15 years (mean 6.15 +/- 3.52 years) with recurrent respiratory infections, were treated with Immucytal, an immunomodulator of bacterial origin, based on membrane proteoglycan fractions plus bacterial ribosomes. The children, selected on the basis of the previous year's clinical score, were treated according to a random design with either Immucytal or placebo, using the same dosage of one puff per nostril plus one puff in the oropharyngeal cavity three times a day, as follows: 1st month: two weeks' treatment, one week wash out, one week's treatment. 2nd, 3rd, 4th months: two weeks' treatment, two week's wash out. Monthly throughout the treatment period the frequency and severity of airway infections episodes were assessed using the same score as for admission. Blood chemistry test, immunological assays (circulating Ig, lymphocyte subpopulations, Merieux Multitest in vivo blastization test) and respiratory tests (spirometry using a pneumotachigraph) were done before and after the treatment. 118/120 children completed treatment; the two dropouts were in the placebo group, one for compliance and the other because of headaches. Respiratory symptoms improved significantly in the actively treated children already from the first month, but not in the placebo group. This improvement consisted of reduction of the respiratory infectious episodes in both the upper and lower airways. No changes were noted in respiratory function parameters. From the immunological viewpoint, there were significant rises in serum IgA and IgM and enhanced skin response tot he Multitest; there was no change in the percentages of different circulating lymphocyte subpopulations.(ABSTRACT TRUNCATED AT 250 WORDS)