The Health Hazard Evaluations and Technical Assistance (HETA) Program responds to requests from employers, employees, employee representatives, and other Federal, State, and local agencies. Through a staff of industrial hygienists, engineers, occupational physicians, epidemiologists, other health professionals, and support personnel, the Hazard Evaluations and Technical Assistance Branch (HETAB) collaborates with appropriate personnel in other divisions of the National Institute for Occupational Safety and Health (NIOSH) to respond to approximately 450 requests for assistance each year. The typical HETA response to a request for assistance results in (l) an evaluation of whether chemical, physical, biological, or other agents are hazardous as used or found in the workplace and (2) the development of recommendations for control procedures, improved work practices, and medical programs to reduce exposure levels and prevent adverse health effects. Health Hazard Evaluation (HHE) site visits are conducted if warranted, and interim and final reports are developed and distributed to employees, unions, management, and relevant Federal and State agencies. When the HETA request is from a Federal, State, or local agency for assistance in investigating another workplace, NIOSH provides only the technical assistance (TA) requested and does not conduct a complete HHE. The results of individual evaluations may trigger wider studies of similar exposures in other settings or may stimulate recommendations for implementation or modification of health standards. Approximately 12,000 evaluations have been completed since the inception of the HETA Program in 1972. Requests received by the HETA Program tend to reflect emerging occupational problems, such as isocyanate exposure and other priority areas. Forty-six isocyanate-related site visits were conducted from 1989 to 2002. The HHE requests came from a variety of sources-including manufacturers of plastic, wood, and automotive products, coal mines, schools, and offices. Sixteen of the requests were made by management, eleven by union, eleven by three or more employees, six by government, and two by management and employees jointly. This document first presents some background information about isocyanate exposures, health effects, analytical methods, and general recommendations that are provided for most isocyanate-related HHEs. The analytical methods section is important because of the complexities and limitations associated with measuring isocyanate exposures. (More detailed information can be gained from the NIOSH Manual of Analytical Methods.) The major portion of this document presents the titles and summaries of the site visits related to isocyantes conducted between 1989 and 2002. In most cases multiple exposures were investigated at the work site; sometimes isocyanate exposures were a primary issue and sometimes not. In many cases, corrective measures were made in response to the evaluation and recommendations made by NIOSH investigators. The purpose of this HHE summary document is to amass the past 14 years of isocyanate-related HHEs in a concise format for easy reference and examination by NIOSH researchers, customers, and partners. Any individual report or letter of interest can easily be requested. The scope and presentation of the individual HHEs vary based on the requesters' needs and the project officers' professional judgment. The document is not meant to be a state-of-the-art review, but instead, it is intended to provide general insight into the types of isocyanate HHE requests received, and HETAB's response to them.