“…This test is a sensitive and reliable method of detecting phenylpyruvic aciduria (Gibbs and Woolf, 1959;Woolf, 1963), which is an early sign of true phenylketonuria (Allen et al, 1964;Berry and Wright, 1967). Some practical difficulties have been emphasized by Hudson and Ireland (1959), but information is lacking on the effectiveness of the napkin test in mass detection programmes.…”