Cold tolerance and biomass estimation of Prosopis species were examined under field conditions. Prosopis africana and P. pallida tolerated several minus 1.5°C freezes but none survived a minus 5°C freeze. P. alba, P. articulata, P. chilensis, P. nigra, and P. tamarugo tolerated several minus 5°C freezes but not a 12-hour below 0°C freeze. Most North American native species P. glandulosa var. glandulosa, P. glandulosa var. torreyana, and P. velutina tolerated the 12 hour freeze with only moderate damage. In general trees with greater productivity belonged to the most cold sensitive accessions but sufficient variability exists to substantially improve Prosopis biomass production on the coldest areas where it now naturally occurs. Forest Sci. 28:556-562.