Abstract. Let (u(t, x), v(t, x)) and (u(t, x), v(t, x)) be two nonnegative classical solutions of {ut = Am + v" , p > 0 v, = Av + uq , q > 0 in some strip ST = (0, T) x R , where 0 < T < oo , and suppose thatwhere «(0, x) and t;(0, x) are continuous, nonnegative, and bounded real functions, one of which is not identically zero. Then one hasIf pq > \ , the result is also true if w(0, x) = v(0, x) = 0 . On the other hand, when 0 < pq < 1 , the set of solutions of (S) with zero initial values is given by u(t;s) = cx(t-sf+ + X)l{X-pQ), v(t;s)=c2(t-s)l:+mi-M), where 0 < s < f, c¡ and c2 are two positive constants depending only on p and q , and (