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. Geographical disaggregation reveals that the benefits have mostly occurred in the North, which also explains higher adoption there. In the North, hybrid adoption caused a 17% increase in household living standards. We conclude that proprietary hybrids can be suitable for semi-subsistence farms and that seed market liberalization has generated positive socioeconomic developments.