The paternity of a newborn with immune thrombocytopenia with unexplained laboratory data was questioned. DNA fingerprinting was employed to test the paternity of the patient. Oligonucleotide (GTG)5 probe labeled with radioactive r-32P-ATP was used to analyze Hinf I digested high molecular weight DNA from the patient and the parents. The results showed that, in the gel, no polymorphic band was specifically transmitted from the putative father to patient, and three bands of the patient could not be traced back to either of the parents. So, non-paternity was confirmed. Such identification not only supported the clinical suspicion, but also directed greater perinatal care in future pregnancies. DNA fingerprinting, unique to each individual, is a powerful technique and con be applied directly to problems of individual identification, including parentage testing.