The PNA-FISH Yeast Traffic Light assay was performed on 54 clinical isolates of yeasts inoculated into blood culture bottles. The assay showed high sensitivity (Candida albicans/C. parapsilosis, 100%; C. glabrata/C. krusei, 92.3%; C. tropicalis, 100%) and specificity (C. albicans/C. parapsilosis, 100%; C. glabrata/C. krusei, 94.8%; C. tropicalis, 100%). Case note review estimated a change in therapy in 29% of cases had the PNA-FISH result been available to the clinician.