The synthesis of two novel series of 1-(4-chlorophenyl)-4-hydroxy-1H-pyrazoles linked to either polysubstituted 1H-pyrazole counterparts through a carbonyl bridge, or to some biologically-active nitrogenous heterocycles by an amide linker, is described. Ten of the newly synthesized compounds were selected by the National Cancer Institute (NCI) in vitro disease-oriented antitumor screening to be evaluated for their antitumor activity. The most active six compounds 2, 3, 6, 7, 13 and 14 revealed a significant broad spectrum of antitumor potential against most of the tested subpanel tumor cell lines at the GI 50 and TGI levels, together with a mild cytotoxic (LC 50 ) activity. The pyrazolinedione analog 7 displayed remarkable growth inhibition and cytostatic effects (GI 50 and TGI MG-MID values 0.67 and 53.8μM, respectively). Compounds 13 (GI 50 , TGI, and LC 50 MG-MID values 0.08, 30.9 and 93.3μM) and 14 (GI 50 , TGI, and LC 50 MG-MID values 0.36, 8.78 and 69.3μM, respectively) proved to be the most active antitumor members identified in this study.