A long-term follow up was begun in 1982 on offspring of mothers who acquired toxoplasmosis during gestation. The 114 newborns were subdivided into 3 groups: (1) 26 born to mothers with certain infection; (2) 51 born to mothers with probable infection, and (3) 37 born to mothers with doubtful infection. There were five infections in the first group (19.2%), three in the second (5.8%) and none in the third. For purposes of data elaboration we considered only the 77 offspring of mothers with certain or probable infection. Of these, 2 infected cases out of 52 (3.8%) were born to mothers with infection in the first trimester of pregnancy, 4 out of 21 (19%) in the second trimester, and two out of four in the third. There were a total of 8 congenital infections (10.4%). Specific IgM antibodies were revealed in five out of eight infected children (62.5%). Infection was symptomatic in two children (2.6% of newborns at risk, 25% of infected cases), both born to mothers with infection in the second trimester. In the other six cases diagnosis was reached by evaluating trends in antibody levels: the percentage of infected newborns was higher in the group of maternal infections untreated (50%) or improperly treated (15.4%), compared to those receiving adequate treatment (6.9%). We suggest considering as infected children presenting specific IgM antibodies and/or antibody titres which do not become negative, even when symptoms are absent. Therapy with spiramycin should be started in all newborns at risk, while the use of sulphamides and pyrimethamine is justified only after the presence of infection is confirmed.(ABSTRACT TRUNCATED AT 250 WORDS)