Oxaliplatin, (trans-R,R-cyclohexane-1,2-diamine)oxalatoplatinum(II), has recently been approved for combination chemotherapy of metastatic colorectal cancer. Oxaliplatin is significantly more active than its trans-S,S isomer and the mixture of both enantiomers. New oxaliplatin analogues, (SP-4-3)-(4-methyl-trans-cyclohexane-1,2-diamine)oxalatoplatinum(II) and (SP-4-3)-(4-ethyl-trans-cyclohexane-1,2-diamine)oxalatoplatinum(II), have been synthesized, and their cytotoxicity has been tested in comparison to oxaliplatin, its corresponding trans-S,S isomer, and the mixture of both enantiomers. In comparison to oxaliplatin, even the trans-R,R/trans-S,S mixture of the 4-methyl and 4-ethyl substituted oxaliplatin analogues have shown an equivalent cytotoxicity in ovarian cancer cells (CH1) and superior antiproliferative properties in colon cancer cells (SW480) in the case of a predominantly equatorial position of the substituent at position 4 of the trans-cyclohexane-1,2-diamine ligand, whereas an axial substitution results in decreased cytotoxic potency.