Two experiments were conducted to determine the effectiveness of Agribrom (1-bromo-3-chloro-5,5-dimethyl-2,4-imidazolidine-dione) for control of algal and fungal slimes on the surface of the growth medium used in the float method for production of tobacco (Nicotiana tabacum L.) transplants in greenhouses. In the first experiment, Agribrom was sprayed weekly on the surface of the growth medium at 0, 10, or 20 mg L^-1 beginning on the date of seeding or at two weeks after seeding. In the second experiment, Agribrom was sprayed weekly at 0, 10, 20, 400, or 800 mg L^-1 beginning on the date of seeding, or at 10 or 20 mg L^-1 beginning two weeks after seeding. Both experiments were harvested after five weeks. Agribrom applications had no effect on the number of plants or biomass production in either test. Agribrom also had no significant effects on algal or fungal growth in either experiment at any treatment rate, regardless of the timing of application. These data indicate that spray applications at concentrations up to 800 mg L^-1 of Agribrom applied at weekly intervals either at seeding or emergence will not control algal or fungal growths in tobacco transplant float-production systems.