The objective of the present research is to study the seasonal morphometric variations of the secondary sexual characters of Aristaeomorpha foliacea and Aristeus antennatus males. Samples were collected from December 1996 to November 1997 using a commercial bottom trawl in a depth range of 446–728 m in the southeastern Ionian Sea (Mediterranean Sea). This is the first attempt to resolve the morphometry of the appendix masculina and appendix interna of these species. Carapace length and lengths and widths of appendix masculina and appendix interna were measured in both species. The relationships between the surfaces of the two appendices and the carapace length in both species were studied. There is a positive allometric growth of these structures in both species. Temporal and bathymetric variation of the above variables are also presented. The possible role of the two appendices in copulation of these two species is discussed.