Growth of Schizosaccharomyces pombe in batch cultures in a commercial defined medium was found to be normal until the last generation before the stationary phase. Approximately one-half the progeny of the last division lysed. Lysis occurred at breaks in the cell wall at cell-plates whose fission was eccentric. Normal culture cycle patterns were obtained when the medium was balanced by addition of either 0.20 mg of l-asparagine per ml or 5.0 mg of KH(2)PO(4) per ml, or both. The lytic effect of growth in the unbalanced medium was compared with similar effects of growth in 2-deoxyglucose. These studies with 2-deoxyglucose in the balanced medium confirmed earlier cytological observations (lysis at all growing points), but showed that the similarities were superficial.