Cationic antimicrobial peptides (AMPs) became a promising alternative to the conventional cancer drugs. We investigated the effects of 5 AMPs (melittin, galanin-mastoparan, cecropins A, B and P1) on the viability of HT-29 and AR-42J carcinoma cells. The viability of the cells was evaluated and used to calculate the AMPs therapeutic index. Also, cellular apoptosis and necrosis were analyzed. Melittin and galanin-mastoparan inhibited HT-29 cells only by necrosis. Melittin, galanin-mastoparan and cecropin A and B inhibited AR-42J cells by both apoptosis and necrosis. These data support the working hypothesis of the specific action of some cationic AMPs on cancer cells.