This testimony concerned primarily workers who may be exposed during release of microbial pesticides into the environment. However, some of the information would apply equally well to workers exposed prior to this phase. NIOSH has conducted a number of studies and developed several reports in the field of biotechnology that the Environmental Protection Agency may find relevant for developing regulations for microorganisms under the Federal Insecticide and Rodenticide Act. The potential for worker exposure would depend on the mechanisms used for delivery of the microorganisms, the composition of the final product, the size of the area to be treated, the intended use of the microorganisms, the capability of the microorganisms to survive and multiply in the environment, and the quantity of microorganisms released. To properly assess the risks posed to workers by environmental release of microorganisms, it is important to address the concept that naturally occurring microorganisms or their products are safe and that genetically manipulated organisms or their products are inherently hazardous or unsafe. Another factor that must be considered is that the degree of change in the genome of the microorganism does not necessarily correlate with physiological properties that this change in genome confers.