We use Bayesian time-varying parameter structural vector autoregressions with stochastic volatility to investigate changes in reduced-form and structural correlations between inventories and either sales growth or the real interest rate in the USA during both the inter-war and post-World War II periods. We identify four structural shocks by combining a single long-run restriction to identify a permanent output shock with three sign restrictions to identify demand? and supply-side transitory shocks. We show that during both the inter-war and post-war periods the structural correlation between inventories and real interest rate conditional on identified interest rate shocks is systematically positive; the reduced-form correlation between the two series is positive during the post-war period, but in line with the predictions of theory it is robustly negative during the inter-war era; during that era the correlations between inventories and either of the two other series exhibit a remarkably strong co-movement with output at business cycle frequencies.