Serum IgG sub-classes levels were measured by radial immunodiffusion with policlonal antibodies in 26 children aged 2 years to 8 years, affected with respiratory recurrent infections. These subjects were controlled and compared with normal children values for age groups. In 10 patients a deficit of IgG sub-classes levels was found, in 7 patients an increase level for IgG1 was detected. These data must be taken in account defining IgG-sub-classes deficiencies in children with respiratory recurrent infection.