We examined the antimicrobial preservative efficacy of nine rigid gas permeable (RGP) contact lens care solutions by challenging them in a laboratory study with both standard test organisms and preservative-resistant strains. Solutions containing polyhexamethylene biguanide (PHMB), such as Boston Advance (15 ppm) and a Boston Advance Enhanced Comfort Formula (5 ppm PHMB + 30 ppm chlorhexidine gluconate [CHG]) were most effective at rapidly killing vegetative cells, killing all bacteria and yeast by 6 hours. Boston Advance only slightly reduced the number ofAspergillus nigerspores during the 28 day study, but Boston Advance Enhanced Comfort Formula reduced the spores by almost 3 logs by 14 days and by 4 logs by 21 days. Thimerosal-preserved Soaclens only reducedStaphylococcus aureusby 1 log at 6 hours, but at 1 day all tested organisms includingS. aureusandA. nigerwere killed. Barnes Hind Gas Permeable Wetting and Soaking Solution, containing 50 ppm CHG, had little effect on adaptedSerratia marcescens or Pseudomonas cepaciaduring the 28 day study. Allergan Wet-N-Soak Plus, containing 30 ppm benzalkonium chloride (BAK), was also unable to kill adaptedS. marcescensorP. cepacia.CIBA Vision Premus (40 ppm BAK) was unable to kill adaptedS. marcescens.Alcon Opti-Free, with 50 ppm polyquaternium-1 (polyquad), did not killP. cepacia.Sherman Stay-Wet 3, containing 0.1% benzylalcohol, was not effective againstS. marcescens(adapted or unadapted),P. cepacia, or A. niger.Sherman DeStat 3, which contains 0.1% benzyl alcohol plus surfactants and five times the concentration of EDTA as in Stay-Wet 3, was able to kill all the vegetative cells by 7 days but did not significantly reduceA. niger.