Seed exchange networks among farmers favor circulation of crop varieties and have been discussed as an effective means of crop diversity conservation. This study aims to document the processes and structure of seed exchange networks of native maize, beans, and squash among farmers and other participating sectors (local market or seed banks), analyzing their influence on agrobiodiversity conservation in the municipalities of Ixtenco and Huamantla, in the Mexican state of Tlaxcala. Through interviews, questionnaires, and social network analysis, nodal farmers were identified. In the maize network, five nodal farmers were detected, the blanco maize being the most commonly exchanged seed. In the bean network, three nodal farmers were identified, with amarillo beans as the most exchanged seed. In the squash network, no nodal farmer was identified. For maize and beans, the greater the number of exchanges, the greater the varieties exchanged. The local market of Huamantla and the Vicente Guerrero seed bank are relevant seed sources. The nodal farmers propitiate circulation of a large number of seed varieties in the exchange networks and contribute to maintenance and conservation of agrobiodiversity.