Rationale The dynamics of the development of T cell-dependent, allergen-specific immunoglobulin changes in early life are not well known. Methods We prospectively studied children with and without atopic sensitization to the Der p 1major allergen. Each group had 15 children, with serum samples obtained at (a) 6 months to 2 years, (b) 2 to 4 years and (c) 4 to 6 years. We determined Der p 1-specific IgE and/or IgG1 concentrations, binding affinities and total binding capacities (concentration × affinity) for each sample. Results In both groups, there were no apparent age-dependent trends in antibody concentrations or binding affinities. Among atopic children, there was also no change with age in Der p 1-IgG1 binding capacity. However, among non-atopics, the rate of increase with age of the total Der p 1-IgG1 binding capacity paralleled the rate of increase for Der p 1-IgE capacity among atopics. Both non-atopic Der p 1-IgG1 and atopic Der p 1-IgE capacities achieved an apparent ‘saturation limit’ by age 6 years. There was also a comparable ‘consolidation’ of responses reflected by a narrowing of the statistical variance of capacity values with age. Conclusions Except for the immunoglobulin classes involved, development of T cell-dependent humoral responses to a non-infectious allergen are similarly regulated in atopic and non-atopic children, with immunoglobulin total binding capacity as the key regulatory element. These original findings in humans suggest that atopy may be an ‘error’ in isotype class switching during an otherwise normal process of antigen recognition and humoral response.