blossom-end rot (ber), a physical common disorder in tomato production, is caused by many factors and the control measures are not well defined. in order to study the effects of ca concentration and osmotic potential (ys) of the nutrient solution (ns), and their interaction, on the number of fruits with blossom-end rot (nfber), nutrient contents and yield in two tomato hybrids, b-52 ball type and anibal ？saladette？ type, two experiments were carried out under net house conditions at the culiacan valley, sinaloa, méxico. in experiment 1, nine treatments resulting from the combination of varying ca concentrations (4.5, 6.75 and 9.0meq·l-1) and ys in the ns (-0.047, -0.072 and -0.097mpa) were evaluated. in experiment 2 other concentrations of ca (7, 9 and 11meq·l-1) and different ys (-0.036, -0.048 and -0.072mpa) were tested. in experiment 1, increasing levels of ca in ns significantly reduced nfber, while decreasing levels of ys increased it. in experiment 2 the fruits with ber had significantly lower contents of ca and p, and higher mg as compared to the fruits without ber. no significant effects in tomato fruit yield were obtained with the ca and ys factors in the two experiments; thus, it is possible to reduce by 50% the investment in fertilizer.