A number of N-bis(trifluoromethyl)alkyl-N'-substituted ureas have been synthesized and evaluated for their in vitro anticancer activity against the human cancer cell lines at the National Cancer Institute (NCI, USA). Marked activity was shown for compounds 4a and 5a. The most sensitive cell lines relative to the tested compounds were: 4a UO-31 (renal cancer, logGI(50) -5.62), HS 578T (breast cancer, logGI(50) -5.50), 5a HCC-2998 (colon cancer, logGI(50) -5.94), NCI-H322M (lung cancer, logGI(50) -5.75) and PC-3 (prostate cancer, logGI(50) -5.66).