Classical asset-pricing models typically assume highly elastic asset demand and therefore imply nearly horizontal demand curves, under which non-fundamental demand shocks should have little effect on prices. However, empirical evidence that contradicts this prediction, together with the growing availability of institutional investors’ portfolio holdings data, has motivated the development of the demand-system approach to asset pricing. Building on this framework, this study estimates the relative price elasticity of demand for Iranian equity investment funds using monthly portfolio holdings data at the fund–stock–month level over the period from April 2019 to March 2025. Fund-level elasticities are identified over one-, three-, six-, nine-, and twelve-month horizons using flow-induced trading pressure constructed from the exogenous component of fund flows as an instrumental variable and are estimated by two-stage least squares (2SLS). The results indicate that equity-fund demand is relatively inelastic and that the corresponding demand curves are not perfectly horizontal. Across most model specifications, estimated elasticities increase with the estimation horizon, while formal inference supports an overall upward, though not fully monotonic, pattern. Across most horizons, small funds exhibit greater demand elasticity than medium-sized funds, which in turn are more elastic than large funds. Controlling for industry fixed effects lowers the estimated elasticity levels but does not materially alter either their horizon-dependent pattern or the ranking across fund-size groups. Overall, the findings suggest that institutional demand elasticity is dynamic, heterogeneous, and inherently dependent on the adjustment horizon.