Preclinical studies have shown that release of silver by different wound dressings varies. The purpose of this in vitro study was to compare the antimicrobial activity of silver alginate (SA) and silver carboxymethylcellulose (SCM) dressings. An- timicrobial activity was tested using nine bacterial strains with log10 reduction and corrected zone of inhibition (CZOI) as- says. Antimicrobial effect was visualized using confocal microscopy (CLSM). Log10 reduction was comparable between both dressings for Staphylococcus aureus NCIMB 9518, Candida albicans ATCC 90028, Finegoldia magna NCTC 11804T, and Pseudomonas aeruginosa NCTC 10662. Log10 reduction was higher for SCM than SA dressing-exposed Escherichia coli (P = 0.035) and P. aeruginosa ATCC 15692 (P = 0.032), and lower for SCM than SA dressing-exposed Streptococcus pyogenes (P = 0.007), Peptoniphilus asaccharolyticus (P = 0.045), and S. aureus NCTC 8325 (P = 0.012). Both dressings were equivalent against four strains (5 to 8 days' activity) in the CZOI assay. SA dressing silver activity lasted >24 hours longer than SCM activity when exposed to C. albicans (9 days' activity), E. coli (7 days' activity), F. magna (5 days' activity), and P. asaccharolyticus (5 days' activity), whereas the SMC exhibited greater persistence against S. pyogenes (13 days' activity). CLSM showed complete kill of S. aureus after 20 hours for both dressings. The results of this study confirm the broad-spectrum, in vitro activity of some dressings containing ionic silver. The in vitro antimicrobial efficacy of both wound dressings was comparable, but clinical studies comparing the efficacy and effectiveness of silver-containing dressings to nonionic silver-containing dressings are needed.