Cytostatic agents often do not discriminate in their cytostatic potential between different tumor cell types in vitro. In this study, several 2-aminothiophene-3-carboxylic acid ester derivatives were discovered that show an unusual cytostatic selectivity for several T-cell (but not B-cell) lymphoma, prostate cancer, kidney carcinoma and hepatoma cell lines. Their 50 % cytostatic concentrations were generally in the higher nanomolar range and were approximately 20- to 50-fold lower for these tumor cell types than for any other tumor cell line or non-tumorigenic cells. The tumor-selective compounds caused a more preferential suppression of protein synthesis than DNA or RNA synthesis and the prototype compound 3 resulted in an accumulation of prostate cancer cells in the G1 phase of their cell cycle. Compound 3 was also shown to induce apoptosis in prostate cancer cells. The 2-aminothiophene-3-carboxylic acid ester derivatives represent novel candidate cytostatic agents to be further explored for their tumor-selective potential.