Pulmonary function parameters were examined in a Malay Muslim population during normal activity and Ramadan fasting conditions. The validity of employing various lung function prediction formulae for the subjects was also assessed. Present findings indicate that the water deprivation regime and resultant dehydration during Ramadan did not cause significant changes in ventilatory functions. Although pulmonary prediction formulae based on Caucasian and African populations were inapplicable to the subjects examined, the equations derived from the neighbouring populations in Singapore could be employed.