Disabilities of patients with coal-workers' pneumoconiosis (CWP) are currently estimated by changes in lung function at rest and the degree of dust equivalents in chest x-ray (ILO-classification 1980). Functional disturbances during exercise are not taken into consideration on a regular basis. We assumed that standardised sub-maximal exercise tests might be useful even in disabled patients to give additional information on functional disabilities of patients with CWP. The impact of low-grade anthracosilicosis on ventilation and gas exchange during exercise was assessed in 20 patients (all male, age 64.55 +/- 3.78 years) and 24 healthy volunteers (all male, age 58.13 +/- 4.68 years, never dust exposed). Data were also analysed according to ILO classification subgroups (group 1: ILO-classification 1/0 to 1/2, n = 11; group 2: ILO-classification 2/1 to 2/2, n = 9). Heart rate (HR), minute ventilation (VE), ventilatory equivalent for O2 (VE/VO2), ventilatory equivalent for CO2 (VE/VCO2), O2 uptake (VO2)CO2 output (VCO2), end-tidal oxygen partial pressure (PetO2), end-tidal carbon dioxide partial pressure (petCO2) and estimated dead space to tidal volume ratio (VD/VT) were determined breath-by-breath during a 50 watts constant work load protocol on an exercise bicycle. The VE/VO2 (patients: 32.9 +/- 4.2; controls: 25.7 +/- 2.9; p < 0.001), the VE/CO2 (patients: 39.4 +/- 4.6; controls; 31.0 +/- 3.9), the VE (patients: 30.1 +/- 5.6, controls: 23.5 +/- 3.0; p < 0.001) and the PetO2 (patients 115.6 +/- 4.8; controls: 99.1 +/- 27.4; p < 0.05) at an exercise of 50 watts were significantly higher in the patients' group, the PetCO2 (patients: 38.4 +/- 4.5; controls: 44.0 +/- 4.1) were significantly lower in the patients' group. The comparison of patients subgroups did not reveal any significant differences between group 1 and group 2. A higher VE/VO2 during 50 watts of exercise is attributable to an increased ventilation/perfusion mismatch. There was no correlation between the radiological grade of the CWP (ILO classification) and the ventilation and gas exchange during exercise. We conclude that a sub-maximal spiroergometry with a 50 watts constant work load might serve as a sensitive and easy to apply procedure add information about the functional impairment in CWP. The exercise test should be included in the evaluation for disability benefits.