Since the early 1990s, liberalization of the seed market in Tanzania has attracted several foreign companies that now market maize hybrids in the country. In this article, we analyze the impacts of proprietary hybrids on maize yields, production, and household living standards. We build on a recent survey of smallholder maize farmers in two zones of Tanzania. Hybrid adoption rates are 48% and 13% in the North and East, respectively. Average net yield gains of hybrids are 50-60%, and there are also significant profit effects.