Investigations of the Gerbich blood group system in Melanesians of Papua/ New Guinea are described. Over 50% of members of certain population groups are Gerbich negative, and anti-Gea (‘naturally-occurring’) is present in about 10% of Ge (a-) people. The distribution of populations with high Ge (a-) incidence is not explicable at present. A Gerbich antibody (anti-Ge 1) with a new specificity has been investigated, and the following phenotypes are now distinguishable: Ge 1, 2, 3 (some Melanesians and almost all others), Ge -1, 2, 3 (some Melanesians), Ge -1, -2, 3 (‘Yus’ type, not found in Melanesians), Ge -1, -2, -3 (Gerbich negatives).