A study was conducted in tomato using an 8 × 8 diallel set excluding reciprocals to quantify the magnitude of heterosis for yield and its five yield components: number of flowers per cluster, number of fruits set per cluster, fruit length, fruit width, fruit weight and fruit yield per plant. Seven accessions and one locally approved variety were crossed in half diallel fashion and the resulting F1 progeny along with their parents were evaluated in a 6 × 6 Tripple Lattice Design at Agricultural Research Institute, Mingora (NWFP), Pakistan during 2007 - 2008 crop season. Highly significant differences were observed among the genotypes for all the studied traits. Highly significant heterosis of positive nature was foundfor flowers per cluster (53.1 and 37.2%), fruits per cluster (38.9%), fruit length (32.7 and 15.5%), fruit weight (48.7 and 45.0%) and yield per plant (34.9%) over the mid and better parents, respectively. Positive significant heterosis was observed for flowers per cluster (7.4%), fruits per cluster (10.0 and 10.0%), fruit length (8.9%), fruit width (8.7 and 7.9%), fruit weight (14.3 and 12.5%), yield per plant (24%) over the mid and better parents, respectively. Four hybrids possessed significantly usefulheterobeltiosis for fruit weight. Three single cross hybrids and four of the parental genotypes were selected for use in subsequent tomato breeding programmes
