Six new 1,4-dihydropyridine derivatives were evaluated in vitro for antimicrobial and cytotoxic effects and in vivo for antineoplastic activity. These compounds inhibited the growth of most of Gram-positive and Gram-negative bacteria at concentrations of 50 and 100 micrograms/ml. Concentrations effective against fungi were somewhat lower (25-50 micrograms/ml). The growth of mycobacteria was inhibited at concentrations of 3.1-25 micrograms/ml. Compound IV inhibited the growth of pathogenic mycobacteria including M. tuberculosis resistant to SM and INH at 3.1 or 6.2 micrograms/ml. In cytotoxicity assays, compound II, IV and V appeared the most active. However, none of the 1,4-dihydropyridine derivatives affected the survival time of mice with P388 and L1210 leukemias or melanoma B16. The growth of subcutaneous tumors of sarcoma 180 was inhibited by compounds I, III, IV and V. The effect was dose related.