Five dolerite dikes emplaced in the Precambrian New Jersey Highlands show little variation in major-element content either within or between them. Based on normative mineralogy, four dikes are quartz tholeiite and one is an olivine tholeiite. Although the Highlands dikes are higher in TiO2 content than has previously been reported for dolerite dikes of eastern United States, the dikes conform to chemical variation trends established for the Palisades Sill and are approximately equivalent in composition to titanium-rich Palisades Sill dolerite which formed when approximately 60 percent of the Palisades magma had solidified. This finding is interpreted to indicate that both the Highlands dikes and Palisades Sill magmas were fractionation products of a more mafic parent magma. Separation of the Palisades Sill magma occurred at an earlier stage in the differentiation process of the parent magma than did the dike magma. Other dolerite dikes of eastern United States with compositions similar to Palisades dolerite were probably also derived from a similar parent magma.