In order to investigate the T cell cytokine profile during age-dependent maturation of the immune response, we evaluated the cytokine expression of CD4+ and CD8+ circulating cells by flow cytometric single-cell analysis after non-specific stimulation in vitro in different age groups of normal individuals, from cord blood to adulthood. Moreover, we correlated these lymphocyte cytokine patterns with the expression/release of CD30, a member of the tumour necrosis factor (TNF) receptor superfamily, which has been suggested to be related to the T helper/cytotoxic (Th(c))2-type immune responses, in order to verify this association in vivo, in non-pathological conditions. The results showed a progressive increase of circulating Th(c)1-type, interferon-gamma (IFN-gamma)- and/or IL-2-producing T cells along with ageing and, conversely, a stable number, although higher than in cord blood samples, of CD4+/IL-4+ T cells in the post-natal groups. In addition, serum levels of soluble CD30 (sCD30) and numbers of circulating CD4+/CD30+ and CD8+/CD30+ T cells were significantly higher in children aged < 5 years in comparison with those found either in cord blood or in blood from both older children and adults. These data support the concept of a progressive polarization of the Th(c) cell cytokine profile towards the Th(c)1 pattern during age-dependent maturation of the immune response. Moreover, the peak of CD30 expression/release in early infancy before the Th(c)1 shifting occurs, although not associated with a significant increase of circulating IL-4+ T cells, raises the question of the possible relationship in vivo between CD30 and Th(c)2-type immune responses.