It is nearly 10 years since Kondo et al.[1] first demonstrated that cord blood lymphocytes can proliferate after in vitro stimulation with allergens. It was also shown that these responses were more common in samples from neonates who subsequently developed atopic disease (atopic asthma, atopic dermatitis, allergic rhinitis, food allergy). Since then there has been a steady flow of publications describing such responses of cord blood mononuclear cells (CBMC), their associations with subsequent childhood atopic disease and their determinants. The study by Marks and colleagues [2] in this issue of Clinical and Experimental Allergy provides a timely opportunity to review issues relating to in vitro CBMC responses to allergens.