Petrological and geochemical investigations of a series of interleaved dikes and lava screens from the Transition Constructional Zone of the Troodos ophiolite are studied to determine whether differences in magnetization of the dike and screen units are the result of primary composition or secondary alteration. Dike and screen units are hydrothermally altered equivalents to the transition alteration zone typified by the presence of chlorite and clays together. Major and trace element results show that the dike and screen units fail within a restricted basalt-basaltic andesite-andesite interval (SiO (sub 2) 46-62 wt %) of the Magma Group A series. Differences in primary composition cannot be responsible for the differences in magnetization. Degree of alteration, rather than style, is a probable explanation for the differences in magnetization. The results of this study indicate that magnetization can be used to interpret lithological sequences present at DSDP/ODP Hole 504B.