A key factor in the planning of any microwave radio-relay system is the repeater spacing achieved for a given quality of service (system outage) due to weather-induced impairment in the transmission path. In the paper the repeater spacing for a high-capacity 19 GHz digital radio-relay system is considered. Naturally emphasis is placed on excess attenuation due to rain, but qualitative judgments of the importance of atmospheric multipath, rain-induced depolarisation, scintillation and snow are also made. Use is made of propagation data and models, and practical observation, derived from related research and development studies. With regard to the quality of service it has been shown that at present it is more appropriate to apportion half of the CCIR recommended nonavailability objective to propagation-induced effects rather than design the system on the basis of reliability criteria.