Abstract
This paper examines whether the reforms introduced by the Italian Stock Exchange from 1991 to 1994 (creation of specialised intermediaries, obligation to trade on the official markets, screen‐based trading and cash settlement) did increase market efficiency. The issue is addressed using both the traditional information efficiency model, which tests market efficiency by verifying the predictability of prices conditional on some information subset, and a microstructure approach that measures efficiency as the distance of the price movements from their efficient components, represented by a random walk process. The joint analysis of daily and intraday data on prices and volumes validates the hypothesis that most of the reforms have increased market efficiency over the sample period, except for cash settlement, which appears to have substantially reduced it.