Guided by the work of Woerdman and Monyakin, we propose rules that allow the electronic transition dipole moment for a transition in one molecule to be determined from that of a similar one in an isovalent species. The rule can be applied to asymptotically allowed and forbidden transitions. We have tested it by applying it in two specific cases: the moments for the A (1)Sigma-->X (1)Sigma and X (1)Sigma-->B (1)Pi transitions in Na-2 are found from those in Li-2, which are asymptotically allowed and the moments for the B-->X transition in O-2, Se-2, and Te-2 which are asymptotically forbidden, are found from moment data for S-2. Transition moments calculated with this rule are within 15% of the available literature values and behavior as a function of internuclear separation is well described. (C) 2003 American Institute of Physics.