We obtain daily data for warrants traded on the Johannesburg Stock Exchange between 1909 and 1922, and for a broker's call option quotes on stocks from 1908 to 1911. We use this new data set to test how close derivative prices are to Black-Scholes (1973) prices and to compute profits for investors using a simple trading rule for call options. We examine whether investors exercised warrants optimally and how they reacted to extensions of the warrants' durations. We show that long before the development of the formal theory, investors had an intuitive grasp of the determinants of derivative pricing. Copyright 2006 by The American Finance Association.