Flies cannot coordinate proper sequence of leg movements for normal walking so that legs on one side of the body or the other become entangled with those behind or in front (Grigliatti et al., 1973); legs held out flat when flies are on a horizontal surface. Mutants cannot climb easily or hang upside down; show poor locomotor behavior in counter current experiments involving agitation of flies and their running toward light (Schmidt-Nielsen and Hall, 1977). Males weak and very poorly fertile. Homozygous females inviable. Two genes, wobA and wobB, are involved in the extreme phenotype (full uncoordinated walking behavior); both factors were extracted from the original strain. In the absence of wobB, walking in wobA flies is only slightly uncoordinated.