The seasonality of inventories and the seasonality and cyclicality of sales of new single-family residences by speculative builders may be formally introduced into a partial production adjustment inventory model of housing starts. The theoretical results include variables that imply an interaction between seasonality and cyclicality. A specification error bias in the estimation of the partial adjustment coefficient is evaluated for models that exclude the interaction between seasonality and cyclicality. Stabilization policy is more complex when cyclical instability changes season to season. In this view, justification is found for a seasonal stabilization policy in housing. Copyright American Real Estate and Urban Economics Association.