A new crystalline anti-tumor agent, compound 593A, has been discovered in fermentation broths of Streptomyces griseoluteus by the human tumor-egg host system which was also used to help guide fermentation and isolation studies. On a weight basis, against the human adenocarcinoma (H. Ad.) # 1 in the embryonated egg, anti-tumor compound 593A is about 100 times as potent as hadacidin, about 4 times as potent as sodium L-tenuazonate, and about one-half as potent as mitomycin C. It also inhibits, in the egg, growth of the human sarcoma (H. S.) #1, and metastasis but not primary growth of the human epidermoid carcinoma (H. Ep.) S3. Anti-tumor compound 593A has the empirical formula C9H11ONaCl. We have discovered a new anti-tumor agent, compound 593A. A product of the actinomycete fermentation, anti-tumor compound 593A was detected in the fermented broth by the human tumor-egg host system which also helped to guide its isolation as a pure crystalline compound. KB cell and bacterial test systems provided supplementary guidance for these studies. Cultures shown to produce anti-metabolite antibiotic activity in their fermentations were among those selected for testing for anti-tumor activity in the egg. The fermented broth of one such culture, isolated from soil collected in the area of Richmond, Union of South Africa, and identified as Streptomyces griseoluteus, was active in the egg, although its anti-tumor and anti-metabolite activities were subsequently found to be from different substances. The anti-tumor substance has been purified, and tentatively designated anti-tumor compound 593A.