Occupational exposure to active pharmaceutical ingredients (APIs), with inhalable exposure limits as low as 1ng/m3, arises in research, development and manufacturing. In most instances it is only possible to make small numbers of measurements of exposure and given the inter- and intra-individual variability it is often difficult to obtain sufficient objective data to make reliable exposure conclusions. The Registration Evaluation and Authorisation of Chemicals (REACH) Regulations 2006 places a greater responsibility on manufacturers of chemicals to prepare Exposure Scenarios (ES) to demonstrate that their chemicals are manufactured, controlled and used in a manner that is safe for their workers, consumers and environment. A validated exposure model is a useful tool in the exposure assessment process and can provide a way of estimating exposure in the absence of sufficient measurement data and in quantitatively assessing these ES. This research aims to further develop and validate an existing exposure model (Cherrie et al., 1996; Cherrie and Schneider, 1999) with the potential to predict airborne exposure from both new and existing operations in the pharmaceutical industry. This deterministic exposure model predicts exposure in a range of pharmaceutical industry scenarios based on information about the work activities, the material being handled, the work environment and exposure controls measures.