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Studies of conformational changes of tRNA de­ pending on the ionic strength of the solution and the nature of the counter ions have become a subject of interest because of the probable role of its different conformational states for the functioning of the tRNA molecule in protein biosynthesis [1]. Results in this field obtained recently e.g. by pulsed nano­ second fluorometry [2] and laser light scattering [3] have caused us to use diffuse X-ray scattering tech­ niques as a tool to obtain more information on the nature of these conformational changes. Small-angle X-ray scattering is a useful technique for studying the conformation of biopolymers in solution, and a number of studies has been carried out on tRNAs already [4-8]. Unfortunately aggregation of the tRNAs, the degree of which seems to vary with the solution conditions, may falsify determinations of parameters describing the large dimensions of the