Does a biological weapon threat exist nowadays? A probability to use pathogenic micro-organisms as a combat agent poses a real threat to a contemporary battlefield. Pathogenic micro-organisms have been used for a long time in wartime as a measure to eliminate the enemy living force. Contagious diseases (also those that appear naturally) decimated troops and often caused greater losses than the combat operations themselves. The article presents orderly arranged and evaluated information concerning the biological weapon development and combat use before World War I, during its course, in the between - the wars period, during World War II and after it. This retrospective view at both remote and recent years is the basis to draw attention to contemporary biological weapon. The author considers the possibilities of purchase, theft or production and then use of biological weapon. The perspectives and conclusions are alarming. In spite of temporary trends, it becomes clear that preventive measures must be taken immediately because eradicating the effects of terrorist attack, during which biological weapon was used, may appear to be impossible.