Drilling fluids represent an important aspect of offshore and land based drilling operations. Periodically, the fluids must be changed or they become old and the spent fluids are disposed of in on-land facilities. Introduction into the environment of the chemically complex fluids has prompted effects research addressing terrestrial and freshwater habitats and their respective biological components. Studies with terrestrial plants in laboratory and field experiments show that the fluids and some fluid components exhibit phytotoxicity properties reducing seed germination, growth and yield. Phytotoxicity in whole drilling fluids is attributed to soluble salt concentrations. Preference/avoidance reactions were observed in experiments with whole drilling fluids are also discussed. The range of lethal concentrations of fluid components in toxicity studies was from < 1 to 75,000 mg/l and that for whole drilling fluids from 0.29 to 85% by volume.