Four of 1,240 cultivated barley lines collected from different regions of the world and 3 of 120 lines of wild barley, Hordeum spontaneum C. Koch, carry spontaneous reciprocal translocations. Break-point positions and rearrangements in the interchanged chromosomes have been examined by both test crosses and Giemsa banding techniques. The four translocation lines in cultivated barley were all of Ethiopian origin and have the same translocation involving chromosomes 2 and 4. The breakpoints are at the centromeres of both chromosomes, resulting in interchanged chromosomes 2S+4S and 2L+4L (S=short arm, L=long arm). A wild barley line, Spont.II, also has translocated chromosomes 2 and 4 which are broken at the centromeres. The resultant chromosomes are, however, 2S+4L and 2L+4S. Another wild barley line, Spont.S-4, has interchanged chromosomes with breakpoints in the short arm of chromosome 3 and the long arm of chromosome 7. In addition, this line has a paracentric inversion in the short arm of chromosome 7 that includes a part of nucleolar constriction, resulting in two tandemly arranged nucleolar constrictions. The third wild barley line, Spont.S-7, has interchanged chromosomes with breakpoints in the long arms of both chromosomes 3 and 6. The translocated chromosome 3 is metacentric and the translocated chromosome 6 has a long arm similar in length to the long arm of chromosome 7.