Hb Villejuif [beta123(H1)Thr-->Ile] is a silent and asymptomatic variant described in 1989 in an 87-year-old woman of French origin suffering from coincidental polycythemia vera. This paper reports the second observation of Hb Villejuif in three related subjects from Montesarchio, Southern Italy. All routine techniques for hemoglobin analysis yielded normal results with the exception of a slight increase in the Hb A2 value. The occurrence of a variant beta-globin was rapidly assessed by liquid chromatography mass spectrometric analysis and the abnormal chain purified by high performance liquid chromatography. The amino acid replacement Thr-->Ile at beta123 was determined by tandem electrospray mass spectrometric analysis of the tryptic digest of the variant beta chain. The corresponding DNA mutation was established as C-->T at the second position of codon 123 (ACC-->ATC) by polymerase chain reaction amplification techniques.