The introduction of antibiotics into therapy during the past ten years has provided a potent weapon against many diseases. The apparent innocuous nature and low toxicity of these drugs qualified them for the label of "miracle" drugs. The antibiotics have altered therapeutics to an amazing degree, and have done much in overcoming the dangers of some types of diseases. However, like high powered bullets, they can be dangerous if uncontrolled. Unlike most other drugs, antibiotics do not have a self-limiting cure-or-kill basis, but have ramifications of undesirable effects which may persist to provide health hazards to an alarming degree not only to animals but to persons working with them. In recent years an increasing number of articles have appeared in the scientific literature on hazards associated with indiscriminate widespread use of these potent drugs. While recognizing the undisputed role of antibiotics in present day therapy, the subject of this report is concerned with undesirable effects and an evaluation of what present indiscriminate use of antibiotics can lead to.