It is supposed that in the time interval (0, infinity) a stochastic process is alternately in states A and B. Denote by alpha (1), beta (1), alpha (2), beta (2),... the lengths of the successive intervals spent in states A and B respectively. In this paper the distribution and the asymptotic distribution of the total time spent in state A (b) in the interval (0,t) are determined in the case where (alpha (1),beta (1)), (alpha (2),beta (2)),... are mutually independent and identically distributed vector variables. (Author)