The nucleotides constitute the back bone structure of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The importance of metal ions in biological processes like transcription, replication and translation reactions are very well established. Therefore, the attention the metal-nucleotide interactions have received, especially during the last decade is not surprising (Marzilli et al 1980; Hodgson 1977; Gillert and Ban 1977; Martin and Mariam 1979; Wilson et al 1982; Orenburg et al 1980; Scheller et al 1981). Among the nucleotides, mostly the nucleotide triphosphates have been studied (Taqui Khan and Rabindra Reddy 1973a, b, 1975, 1976; Taqui Khan and Martell 1967; Wallas 1958). However, very little is known on metal-mononucleotide interactions and that too with bivalent metal ions. The data with metals of higher oxidation states are not available in the literature. Therefore, it was considered important to investigate the interaction of 5'-cytidine monophosphate with various metal ions. Earlier we have studied the interaction of 5'-cytidine monophosphate with transition and alkaline earth metal ions along with other related systems (Rabindra Reddy et al 1985). In the present manuscript, we have extended our investigations to the trivalent lanthanides to study the influence of charge on the stability of the mononucleotides.