Thirty Schiff bases of hydroxysemicarbazide (Ar-CH=NNHCONHOH) have been synthesized and tested against L1210 murine leukemia cells. The IC(50) values were found to be in a range from 2.7 x 10(-6) to 9.4 x 10(-4) M. A total of 17 out of the 30 compounds had higher inhibitory activities than hydroxyurea (an anticancer drug currently used for the treatment of melanoma, leukemia, and ovarian cancer) against L1210 cells. Six compounds with IC(50) values in micromolar range were 11- to 30-fold more potent than hydroxyurea (IC(50) = 8.2 x 10(-5) M). The partition coefficient (log P) and ionization constants (pK(a)) of a model compound [1-(3-trifluoromethylbenzylidene)-4-hydroxysemicarbazide, 1] were measured by the shake-flask method, and the measured log P was used to derive Hansch-Fujita pi constant of -CH=NNHCONHOH. On the basis of the newly derived pi and those of other moieties, the partition coefficients (SlogP) of the other 29 compounds were calculated by the summation of pi values. Quantitative structure-activity relationship (QSAR) analysis showed that, besides the essential pharmacophore (-NHCONHOH), hydrophobicity (SlogP), molecular size/polarizability (calculated molar refractivity), and the presence of an oxygen-containing group at the ortho position (I) were important determinants for the antitumor activities. In conclusion, the results obtained in this study show that several Schiff bases of hydroxysemicarbazide are potent inhibitors of tumor cells and warrant further investigation as cancer chemotherapeutic agents.