Abstract Antimicrobial peptides (AMPs) are produced by all forms of living organisms and represent a novel class of antibiotics to treat infectious diseases. In this study, 29 AMPs of varying length and characteristics were synthesised chemically and were evaluated for their ability to inhibit the growth of Bacillus globigii, Bacillus anthracis and Burkholderia thailandensis. Amongst the peptides tested, sheep myeloid antimicrobial peptide-29 (SMAP-29) was the most potent, inhibiting both B. globigii and B. anthracis at submicromolar concentrations. However, SMAP-29 was less effective against B. thailandensis (minimum inhibitory concentration of 71 μM). Haemolytic activity and cytotoxicity were determined using human blood cells and human embryonic kidney 293S cells, respectively. Most of the peptides tested showed varying degrees of haemolytic activity and cytotoxicity, with SMAP-29 being highly haemolytic and cytotoxic under the conditions tested. Nevertheless, strategies to reduce toxicity whilst maintaining high antimicrobial activity are worth pursuing in light of the results obtained.