Abstract: The present invention pertains to methods of monitoring mycoplasmal growth whereby a culture of mycoplasmal cells is contacted with a fluorescent nucleic acid-binding agent under conditions which allow the agent to selectively bind to mycoplasmal nucleic acid. The amount of fluorescence associated with the mycoplasmal nucleic acid indicates the number of mycoplasmal cells in the culture. The fluorescence of the culture is typically read using a fluorometer which correlates with colonial growth on agar. A particularly preferred fluorescent nucleic acid-binding agent is ethidium bromide. The present invention further pertains to methods of determining the effectiveness of an antimycoplasmal antibiotic.