On the basis of pharmacophoric modelling studies of existing NNRTIs, a series of isatin beta-thiosemicarbazone derivatives was synthesized and evaluated for their anti-HIV activity in HTLV-III(B) strain in the CEM cell line. Three compounds showed significant anti-HIV activity, whereupon compound 6 was found to be the most active compound with an EC(50) value of 2.62 microM and a selectivity index of 17.41, while not being cytotoxic to the cell line at a CC(50) value of 44.90 microM. Other tested compounds exhibited marked activity below their toxicity threshold.