A study was made of factors affecting flowering and fruit set in pepper plants grown from seed. The duration of the initial vegetative phase of growth was prolonged when radiant exposures were low, as in the winter or when shading was used in the summer. The change from vegetative to reproductive development was also delayed by a reduction in night temperatures from 20�C to 13�C. It is suggested that radiant exposure and night temperature affected flower initiation through effects on the rate of growth and development of the whole plant rather than on processes specific to the control of flowering. In experiments designed to examine responses to long and short photoperiods, results varied with the source of illumination used in providing the long-day treatments. Extension of an 8h day to 18h by the use of low intensity illumination from tungsten-filament lamps delayed flower initiation by a few days but when warm-white fluorescent lamps were used to extend the day the time to flower initiation was unaffected. A proportion of the flowers initiated stopped growing in the bud stage and aborted. Conditions found to be conducive to flower abortion were low radiant exposures, high night temperatures, long-day treatments produced by the use of tungsten filament lamps and infrequent watering. Pollination and fertilization were not prerequisites for fruit set since parthenocarpic fruit development could occur. The incidence of parthenocarpy was high when night temperatures were low. Low radiant exposures, high night temperatures and infrequent watering were unfavourable to fruit set and led to increases in the proportion of flowers that were shed after opening. Under some conditions the proportion of open flowers that set fruits could be increased by pruning the plants to reduce the number of leading shoots or by spraying with B-naphthoxyacetic acid.