A multilaboratory collaborative study was performed in order to propose quality control limits for posaconazole disk diffusion susceptibility tests on Mueller-Hinton agar supplemented with 2% glucose and 0.5 mu g of methylene blue per ml. Replicate tests were performed on three lots of prepared media using 5-mu g posaconazole disks in each of eight laboratories to generate data to propose quality control zone diameter ranges for tests of Candida albicans ATCC 90028 (24 to 34 mm), C. parapsilosis ATCC 22019 (25 to 36 mm), C. tropicalis ATCC 750 (23 to 33 mm), and C. krusei ATCC 6258 (23 to 31 mm).