The objective of this study was to find a model to describe the relationship between the occurrence of pleural plaques and exposure to asbestos. A simple model based on the cumulative exposure was postulated and empirically tested on shipyard workers occupationally exposed to asbestos. Exposure time was used to approximate the cumulative dose. It was found that the incidence of pleural plaques could be described as K(t-w)a where 't' is time since onset of exposure; 'K' is a constant that would depend on the level of asbestos exposure; 'w' is a latency period and was around 13 years; 'a' is a constant that was 0.4. In subgroups of the workers, i.e. plumbers, fitters and platers, 'a' was 0.4, 0.6 and 0.2 respectively.