Nalidixic Acid (NA)* incorporated into a polyvinyl chloride film has recently been proposed as a UV-A radiation dosimeter. A trial, in which two different batches of NA film were exposed to both solar simulating and monochromatic 330 nm radiation is described. With both batches of film a linear relationship was observed between the UV-A fluence derived from the NA film and the fiuence determined with conventional electronic radiometric equipment. There was, however, considerable batch variation in response to UV-A radiation. Corrections may be made for batch differences. If the batch response can be standardized, our results would support the use of NA film as a simple routine method of measuring UV-A radiation.