A 10 year old boy with Proteus syndrome presented with a pericardial effusi
on of unknown aetiology. Immunological investigation revealed low serum Ige
and IgA, accompanied by low levels of specific antibodies to pneumococcal
and haemophilus type B polysaccharides. Circulating lymphocyte surface mark
er profile revealed T and B cell lymphopenia. This is the first report of h
ypogammaglobulinaemia occurring in the Proteus syndrome.