Fifty-one dominant female sterile (Fs) mutations linked to the third chromosome of Drosophila melanogaster are described. EMS induced Fs mutations arise with the frequency of one Fs per about 2500 recessive lethals. Complementation analysis of the revertants showed that these Fs mutations represent 27-34 loci, about 60% of the third chromosome units mutable to dominant female sterility by EMS. The Fs mutations were mapped on the basis of mitotic recombination induced in the female (in 16 cases also in the male) germ-line. Behavior of the revertants and the Fs+ germ-line clones demonstrate the gain-of-function nature of the Fs alleles. With two exceptions, the Fs(3) mutations are germ-line dependent. Novel phenotypes appeared in most of the Fs mutations. With eight exceptions, the Fs(3) mutations are fully penetrant, in some cases with variable expressivity. One of the Fs(3) mutations is a non-ovary-dependent egg retention mutation, two others alter egg shape, and 27 bring about arrest in development at about the time of fertilization. In 21 of the Fs(3) mutations embryos develop to the larval stage of differentiation; this group includes 5 new alleles of Toll and 4 of easter.