A path model of structural change and growth for complex organizations was constructed to investigate relationships between organizational size and spatial, vertical, and horizontal complexity. It was estimated using data from a heterogeneous sample of federal and state agencies located in California. The findings alter and extend the explanatory scheme and the generalizability of Blau's formal theory of differentiation, as well as recent modifications of that theory. Several new relationships were considered. They suggested two things: certain established propositions may be unique to organizational types; and they support several alternative propositions about organizational growth and change.