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A new crystalline antibiotic designated PSX-1 has been isolated from the fermentation broth of Penicillium stipitarum THOM. Antibiotic PSX-1 is a neutral reddish substance melting at 33-34'C, containing only C, H and 0. (2max. 207 and 270 nm in methanol). The other crystalline antibiotic identified as duclauxin was isolated from the filtrate of the above-mentioned strain.Both antibiotics showed an inhibitory effect on EHRLICH ascites carcinoma (EAC), lymphadenoma L-5178 and sarcoma 37.The production of potential cancerostatic substances in a larger group of Fungi imperfecti was studied, using a method based on inhibition of incorporation of 14C-labelled adenine and l-valine into EAC cells1). Penicillium stipitatum THOM was one of the tested cultures whose filtrates showed an observable activity on EAC cells. The known metabolites of this mould-tropolonesstipitatic acid2), stipitatonic acid3) and stipitalid4) were isolated from the filtrates of given strain as well as the ethyl ester of stipitatic acid5,6) showed no activity in the used screening test.The cancerostatic activity of filtrates detected, depended on the presence of some metabolites, yet unknown, of non-tropolone character. Production and IsolationA medium containing 9 % sucrose, 1 % corn-steep liquor (65 % dry weight), 0.2 % NaNO3, 0.1 % KH2PO4, 0.05% KCl, 0.05% MgSO4.7H2O and 0.001 % FeSO4.7H2O adjusted to pH 6.3 was found to be suitable for the growth of inoculum. Strain CBS 375.48 was cultivated in 100 ml of the medium, inoculated with 2.5 ml spore suspension, and placed in 500 ml shake flasks at 28°C for 42 hours. Four hundred ml of vegetative inoculum thus prepared was inoculated in 10 liters of the same medium in a small fermentor of 20-liter volume and cultivated for 30 hours at 28°C with aeration of 7.5 liters/min. and stirring at 300 r. p. m. Sixteen liters of the culture thus obtained were inoculated into 300 liters of medium containing 5 % glucose, 0.2 % NaNO3, 0.1 % KH2PO4, 0.5 % KCl, 0.05 % MgSO4.7H20 and 0.001 % FeSO4.7H2O adjusted pH to 6.3 in a stainless steel fermentor of 500-liter volume. The fermentation was continued for 120 hours at 28°C with aeration of 225 liters/min. and stirring at 220 r. p. m.The mycelial cake was collected by filtration. The clear filtrate (190 liters, pH 4.0) was stirred for 30 minutes with 90 liters of tetrachloromethane at 22-24°C. The tetrachloromethane layer was separated, clarified by centrifugation and dried by filtration through anhydrous Na2SO4. The obtained solution was concentrated under reduced pressure to 500 ml and the concentrate was allowed to stand at 5°C overnight. From the concentrated extract the substance X-2 with a strong

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