The Knoevenagel reaction between 2-indolinones and 2-chloroindolaldehydes gave 3-(2-chloro-3-indolylmethylene)1,3-dihydroindol-2-ones which were tested as potential antitumor agents on cultures of HeLa cells. 2-Chloro derivatives with at least one unsubstituted NH group, are promising candidates for further investigation.