The variation and stability of vinyl chloride monomer (75014) (VCM) collected on charcoal tubes were determined and the interlaboratory test results were compared to establish standard reference VCM charcoal tubes. Four charcoal tubes containing 2 concentrations of VCM with 2 tubes at each concentration were analyzed by 42 different laboratories. Replications on each tube were performed to furnish error estimates for sample generation, instrument precision, and interlaboratory error. Statistical analysis showed that replication error varied from 0.85 to 1.43 percent and was due to noise, drift, integration, and syringe reading error. Sample error varied from 2.48 to 4.45 percent and arose from variation in permeation rate, individual charcoal tubes, and temperature and pressure of the system. Interlaboratory systematic error varied from 14.8 to 18.16 percent and was due mostly to callibration errors. The author concludes that the permeation method is adequate to generate accurate, uniform, and stable VCM reference samples, and can be used to evaluate instrument performance, calibration curve, and analytical procedures.