Silver-containing dressings are considered fundamental to the management of infected acute and chronic wounds, specifically burns. The aim of this study was to determine both the spectrum of activity and efficacy of an Alginate/CMC Silver Dressing (ACSP) on planktonic microorganisms by conducting a 21-day repeat-challenge log reduction study. ACSP was found to have a microbiocidal effect, for up to 21 days, on all bacteria and yeast challenged. The results demonstrated an antimicrobial efficacy similar to Hydrofiber Silver Dressing's (HSD) up to day 14 for each microorganism tested. However, following a second reinoculation of microorganisms at day 14, ACSP showed antimicrobial efficacy superior to HSD's against a number of opportunistic pathogens, which included Pseudomonas aeruginosa and Candida albicans. The ACSD maintained its antimicrobial action against all microorganisms over the 21-day study period.