Laboratory and field trials were conducted in mushroom crops to assess the possibility for biological control of Lycoriella solani (Winnertz) which infests cultivated mushrooms (Agaricus bisporus). Laboratory trials in mini bags containing mushroom compost showed that the predatory mite Hypoaspis miles (Berlese) could suppress populations of its prey to very low levels. To assess the possibility for biological control of L. solani on a larger scale, trials were carried out in commercial growing bags on a mushroom farm. The mite suppressed its prey to very low densities. All instars of the mite were recorded in the treatments, whether introduced with L. solani or without. The number of H. miles was higher when introduced with L. solani than without. Crop yield was higher where the predators had been introduced at spawning, and more mushrooms were produced when predators were introduced at the spawning and casing period.