The ambient nitrogen dioxide concentration in the museum environment was measured by a passive sampler designed to minimize the effect of wind speed on the sampling, on a monthly average basis for one year. It was found that the nitrogen dioxide concentrations generally ranged between 10-20ppb in the exhibition room. Air conditioning was found to be effective in controlling ambient nitrogen dioxide concentration, while a kerosene stove raised the nitrogen dioxide concentration to a very high level. A closed environmental system is also useful in making the nitrogen dioxide concentration lower. Fading test pieces dyed by purpurin, brazilin, myricetin, and tannin, all selected from Japanese traditional dyestuffs, were exposed to the museum environment for three, six, and twelve months. As a result of dose-response evaluation, on the basis of nitrogen dioxide concentration and DELTAE, the correlation between them was found to be fairly good, although DELTAE may also be influenced by other environmental fading factors. The nitrogen dioxide dose is considered to be a useful comprehensive index for expressing environmental fading factors in Japan. -- AATA