An intercomparison of visual diffuse transmission density measurements of photographic and x-ray film step tablets was completed by two national metrology institutes, the National Institute of Standards and Technology, USA, and the Physikalisch-Technische Bundesanstalt, Germany. The samples were measured by three reference densitometers according to procedures described in international documentary standards. The instruments are well characterized with estimates of their measurement uncertainties. The systematic differences between the density measurements were less than 0.010 for the photographic films and 0.015 for the x-ray films for densities as great as 3.3.