The XbaI Restriction Fragment Length Polymorphism (RFLP) of the APOB gene at codon 2488 was investigated in a sample group from Southern Italy (165 subjects), taken from a population characterized by a low average level of cholesterolemia. The X2 allele (presence of XbaI cutting site), that in several groups was found to be associated with increased cholesterolemia, showed in Southern Italians a frequency of 39% which is significantly (P much less than 0.001) lower than that found in the majority of the Caucasoid groups so far tested (50%). However, an analysis of both cholesterol and APOB serum levels performed in a sample of 82 subjects, homogeneous for sex and age did not reveal any significant association between lipidemic parameters and APOB-XbaI genotypes.