In a follow-up study the prevalence of chronic respiratory symptoms and changes in ventilatory capacity were followed over a period of three years in 38 female and 28 male hemp workers in a textile industry. The prevalence of all respiratory symptoms was found to be increased. Significant acute reductions of ventilatory capacity were recorded during the work shift. The measured ventilatory capacity values were significantly decreased in comparison to predicted normal values. The mean annual decline of FVC (range: 0.014-0.065 L), FEV1 (range: 0.041-0.068 L), FEF50 (range: 0.020-0.220 L/s) and FEF25 (range: 0.030-0.140 L/s) was considerably greater than in healthy non-exposed subjects. The mean annual decline of all tests was considerably larger in workers with the symptoms of byssinosis than in those without such symptoms. Our data suggest that long-term exposure to hemp dust may cause the development of chronic respiratory symptoms and impairment of ventilatory capacity.