Click on title above for a wikipedia overview and be sure to note the post-ban section which states;
Both the U.S. bio-weapons ban and the Biological Weapons Convention restricted any work in the area of biological warfare to defensive in nature. In reality, this gives BWC member-states wide latitude to conduct BW research because the BWC contains no provisions for monitoring of enforcement. The treaty, essentially, is a gentlemen's agreement amongst members backed by the long-prevailing thought that biological warfare should not be used in battle.
After Nixon declared an end to the U.S. bio-weapons program debate in the Army centered around whether or not toxin weapons were included in the president's declaration. Following Nixon's November 1969 order, scientists at Fort Detrick worked on one toxin, Staphylococcus enterotoxin type B (SEB), for several more months. Nixon ended the debate when he added toxins to the bio-weapons ban in February 1970. The U.S. also ran a series of experiments with anthrax, code named Project Bacchus, Project Clear Vision and Project Jefferson in the late 1990s and early 2000s.
In recent years certain critics have claimed the U.S. stance on biological warfare and the use of biological agents has differed from historical interpretations of the BWC. For example, it is said that the U.S. now maintains that the Article I of the BWC (which explicitly bans bio-weapons), does not apply to "non-lethal" biological agents. Previous interpretation was stated to be in line with a definition laid out in Public Law 101-298, the Biological Weapons Anti-Terrorism Act of 1989. That law defined a biological agent as:
any micro-organism, virus, infectious substance, or biological product that may be engineered as a result of biotechnology, or any naturally occurring or bioengineered component of any such microorganism, virus, infectious substance, or biological product, capable of causing death, disease, or other biological malfunction in a human, an animal, a plant, or another living organism; deterioration of food, water, equipment, supplies, or material of any kind...
According to the Federation of American Scientists, U.S. work on non-lethal agents exceeds limitations in the BWC.
 Agents and weapons
When the U.S. BW program ended in 1969 it had developed seven mass-produced, battle-ready biological weapons in the form of agents that cause: anthrax, tularemia, brucellosis, Q-fever, VEE, and botulism. In addition Staphylococcal Enterotoxin B was produced as an incapacitating agent. In addition to the agents that were ready to be used the U.S. program conducted research into the weaponization of more than 20 other agents. They included: (among others) smallpox, EEE and WEE, AHF, Hantavirus, BHF, Lassa fever, glanders, melioidosis, plague, yellow fever, psittacosis, typhus, dengue fever, Rift Valley fever (RVF), CHIKV, late blight of potato, rinderpest, Newcastle disease, bird flu, and the toxin ricin.