Twelve varieties of tomato of economic importance and their hybrids (including reciprocals) were studied in four environments: inside and outside of greenhouses and with and without plastic mulching. Seven characters were recorded per plant per environment: (1) total yield, (2) fruit weight, (3) locules/fruit, (4) fruits/cluster, (5) earliness in maturity, (6) earliness in harvesting and (7) leaves between clusters. There was an almost general tendency for hybrids to show higher values than the parentals for characters (1), (4) and (7); the opposite was true for (2) and (3), even when the differences were not statistically significant at the 5% level. Environments were always highly significant; the effect of the greenhouse explained most of the variation. Genotype-environment interaction by regression analysis showed that the performance of the hybrids was generally higher than that of the parents for characters (1), (4) and (7). Total yield was higher, in general, in the most protected environments. Locules per fruit was very constant but when interaction did exist, the number of locules was higher in the less protected environments. Hybrids interacted with environments more strongly than parent lines. Earliness was the most environmental dependent characteristic the choice of early harvesting being irrelevant. Some of the hybrids obtained seem promising from a commercial point of view.