Two independent, three-dimensional structures of yeast tRNAAsp, mainly differing by the conformation of the D loop, have been obtained from a multiple isomorphous replacement (MIR) X-ray analysis at 3.5-A resolution. The folding of the ribose-phosphate backbone is similar to that found for tRNAPhe; major differences concern the relative positioning of the acceptor and anticodon stems, and the conformation of the loops in the two molecules. Crystal packing involves self-complementary GUC anticodon interactions.