Durable-goods monopolists face special problems because the sale of their products creates a secondhand market not controlled by the monopolist. To the extent the monopolist is able to rent his product rather than sell it, or to make binding promises about his future production, such problems are ameliorated. Given the inability to do the above, the monopolist is led to producing goods less durable than those produced by either competitive firms or monopolist returns. A reverse Averch-Johnson result--that monopolist sellers may invest less in fixed costs (including plant modernization and research and development) than would the renters--is shown. It is also shown that, even though sellers have less monopoly power than renters and nondurable-goods monopolists, it is possible that the seller will cause a greater deadweight loss than the other types of monopolies.