We examined by immunoblotting sera from 39 latex-allergic patients, 19 from USA and 20 from Finland, including 15 children with spina bifida and 5 children with other congenital anomalies, for IgE antibodies to natural rubber latex (latex) antigens. IgE antibodies in 10 of the 12 (83%) US spina bifida patients and in 2 of the 3 Finnish spina bifida patients recognized a previously undescribed 27-kD antigen which, together with a 14- and a 20-kD peptide, appeared to be a major latex allergen. Two patients with other congenital anomalies, one from the US and one from Finland, also demonstrated anti-27-kD bands. IgE antibodies to the 27-kD antigen were not detected in other latex-allergic patients from the US or Finland although most of them showed IgE binding to 14- and/or 20-kD latex antigens. All 21 controls, including 3 spina bifida patients with no evidence of latex allergy, gave negative immunoblot results. This observation suggests that patients with spina bifida or other congenital anomalies who have been subject to multiple operations and other invasive therapeutic procedures may have been exposed to different antigenic source materials than other latex-allergic patients.