[en] Through parallel phytotron, greenhouse and field analyses 23 short-day tolerant early mutants of barley have been isolated from 59 greenhouse-tested genotypes and several hundred others cultivated under field conditions. One mutant, carrying the gene (allele) mat-a⁸, was released under the name of Svaloef's Mari. Later, after gene recombination, it gave rise to several valuable varieties. Mari and its derivative Mona, which also possesses the gene mat-a⁸, are adapted to widely different climatic constellations and produce very high yields under optimal conditions. Short-day tolerant mutants can easily be isolated and identified by simple greenhouse techniques. Most of such mutants belong to the locus mat-a. Different degrees of short-day tolerance exist. No certain case of a locus-b mutant being short-day tolerant was found. Previous conclusions to the contrary are incorrect. (author)