Most medical microbiology laboratories in the Netherlands have switched from direct potassium hydroxide microscopy and culture to polymerase chain reaction (PCR) testing when diagnosing dermato- and onychomycoses and Candida species in human dander, hair and nails. The predictive value of a PCR test is in most cases higher than the predictive value of KOH microscopy and culture in diagnosing or ruling out a fungal infection and should therefore replace traditional diagnostics in routine care. KOH microscopy and culture should be reserved in cases of therapy failure and suspected false negative PCR testing. An application for a PCR should be performed if there is any doubt about the clinical diagnosis. The application must be accompanied by sufficient clinical information from the patient to enable the microbiologist to determine whether the PCR test used is appropriate.