The automatic milking process is represented by means of a model which allows the factors affecting the capacity of an automatic milking system to be studied. The main factors investigated are the times required for cow movements, milking processes and robot motions. With one robot serving two stalls, the idle time of the robot arm was 54%. From an analysis of the milking cycle, it is shown that the robot arm can serve up to four milking stalls in-line. The model showed also that the capacity of an automatic milking system with two stalls in-line, can be increased from 11·7 to nearly 15·4 cows h h-1 by increasing the robot speed, by executing some milking processes simultaneously and by changing the sequence of milking processes. If the robot is available for milking for 20 h, 308 milkings could be carried out. Thus, with a milking frequency of four milkings per cow per 24 h for the whole herd, the milking robot could serve nearly 80 cows. The possibilities of alternative arrangements such as a double tandem and a rotary tandem milking parlour, are also tested with the model.