This research was designed to study the effects of milking practices upon the deterioration of natural rubber liners. Winter rations appear to produce a more severe rate of blistering than either summer pasture or ration. Cleaning seemed to have little effect upon rate of blistering. Storage in 10% lye solutions increased the time to blister. Pure fatty acids were shown to produce blistering. Udder ointments and mastitis treatments used in this study had no appreciable effects on blistering of rubber.