[en] The theory and analytical procedures in Instrumental Neutron Activation Analysis (INAA) are discussed. Application of the method to the determination of sixteen trace elements: Na, K, Mn, Sm, La, Fe, Th, Sc, Co, Ba, Rb, Br, Sb, Cs and Ta in some rock samples from Ugep in the Lower Benue Region of Nigeria, is described. The high radioactivity observed in some of the samples analyzed has been associated with the higher-than-normal concentrations of Th and K in the samples. Also, Ba and Fe concentrations in some of the samples were found to be anomalous when compared with average expected values in normal sedimentary rocks. (author) 12 refs.; 3 tabs