This report describes anamnestic, physical and biochemical data in the neonatal period which have led to the diagnosis of an inborn error of metabolism in 12 children. Even in hospital laboratories without facilities for elaborate biochemical assays, adequate investigations permitting timely referral of the patient to a more specialised hospital can often be carried out. Most important is the constant awareness of the pediatrician in case of serious illness which cannot be easily explained by more common causes. The similarity of the clinical presentation and often the coexistence of neonatal sepsis and inborn error of metabolism are stressed. Even when treatment is not possible or has not been successful, a correct diagnosis is important for genetic counseling and antenatal diagnostic procedures.