A series of field evaluations was performed to estimate the overall uncertainty of three manufacturers' passive monitors (Assay Technology Model 541 and 546, 3M Model 3520, and SKC Model 575-001) to determine methylene chloride (MeCl2) concentrations. Area samples were exposed in a pharmaceutical production facility at five MeCl2 air concentrations for both permissible exposure limit (PEL) and short-term exposure limit (STEL) periods. A specially designed evaluation chamber was used to concurrently expose six of each type of passive monitor while concurrently collecting six active samples from locations surrounding the dosimeter array. The active samples were used to estimate the actual concentration during the evaluation period. The precision, bias, and overall uncertainty were estimated for each monitor type at concentrations bracketing the Occupational Safety and Health Administration proposed exposure limits. The actual MeCl2 concentrations for the PEL sampling periods ranged from 0.9 to 63 ppm. The pooled overall uncertainty results for all the passive monitors evaluated under PEL sampling conditions met the NIOSH accuracy recommendations. Pooled overall uncertainty for PEL evaluations for the monitors were: Assay Technology Model 546 +/- 17%; 3M +/- 13%; and SKC +/- 17%. Actual MeCl2 concentrations for the STEL sampling periods ranged from 14 to 357 ppm. Pooled overall uncertainty results for Assay Technology and 3M monitors evaluated under STEL sampling conditions met the NIOSH accuracy recommendations; however, the SKC passive monitor was slightly greater than the NIOSH recommendation. Pooled overall uncertainty for STEL evaluations for the monitors were: Assay Technology Model 541 +/- 18%; 3M +/- 16%; and SKC +/- 27%.