The aim of this study was to evaluate the performance characteristics of 6 intact parathyroid hormone assays: Access 2 (Beckman Coulter, Fullerton, CA), ARCHITECT i2000(SR) (Abbott Diagnostics, Abbott Park, IL), ADVIA Centaur (Siemens Healthcare Diagnostics, Deerfield, IL), Modular E170 (Roche Diagnostics, Indianapolis, IN), IMMULITE 2000 (Siemens Healthcare Diagnostics), and LIAISON (DiaSorin, Stillwater, MN). Sample collection tubes and storage conditions were compared. Imprecision studies were performed using commercial quality control materials. Linearity was assessed using pools prepared from samples. For method comparison, serum and EDTA plasma samples were tested by all methods, and the ARCHITECT was used as the comparison method. Reference intervals were determined using various vitamin D cutoffs. The types of collection tubes and storage conditions are more important for some methods than others. Total coefficients of variation were 10.9% or less. The maximum deviation from the target recovery for linearity ranged from 5.0% to 82.2%. Bland-Altman plots demonstrated percentage biases ranging from -36.3% to 24.4%. The lower limit of the reference interval was not influenced by vitamin D status, whereas the upper reference limit was affected.