A bull is a graph which is obtained by attaching two edges to two vertices of a triangle. A bull-design of order n is an ordered pair (X,A), where X is the vertex set of Kn and A is an edge-disjoint decomposition of Kn into copies of bulls. In this paper, it is shown that a bull-design of order n can be embedded in a bull-design of order m if and only if m≥3n/2+1 or m=n. This produces a generalization of the Doyen–Wilson theorem for bull-designs.