A new series of 5-nitro-1H-indole-2,3-dione-3-thiosemicarbazones (3a-k) obtained by condensation of 5-nitro-1H-indole-2,3-dione (1) with N-substituted-thiosemicarbazides (2a-k) were treated with morpholine or piperidine and formaldehyde to yield 1-morpholino/piperidinomethyl-5-nitroindole-2,3-dione-3-thiosemicarbazones (4a-m). The structures of all the compounds were determined by analytical and spectral (IR, 1H-NMR, EIMS) methods. Compounds 3b, 3c, 3f, 3k, 4a, 4c, 4f and 4l chosen as prototypes were evaluated in the National Cancer Institute's 3-cell line, one dose in vitro primary cytotoxicity assay. All the compounds that passed the criteria for activity in this assay were scheduled automatically for evaluation against the full panel of 60 human tumour cell lines at a minimum of five concentrations at 10-fold dilutions. Sulphorhodamine B (SRB) protein assay was used to estimate cell stability or growth. The most active compound was found to be 1-morpholinomethyl-5-nitroindole-2,3-dione-3-N-(chlorophenyl)thiosemicarbazone (4l). This compound demonstrated the most marked effects in the National Cancer Institute's 60 human tumour cell line in vitro screen on a non-small cell lung cancer cell line (HOP-62, log(10)GI(50) value <-8.00) and on leukaemia cell lines (HL-60(TB), log(10)GI(50) value -6.30; MOLT-4, log(10)GI(50) value -6.18).