This reports a research work that measured the social capital of indigenous Kanakaney and Ibaloi vegetable growers and traders in seven highland communities of Benguet, in the Cordillera region, Philippines. The social capital index was calculated using an additive equation. The equation consists of measurable variables such as formal associations, trust, collective action and satisfaction and optimism. Six factors explaining social capital were extracted. Tests were used to check for relationships between social capital indicators and exogenous variables such as gender, educational attainment, religion, age and ethnicity. The effect of social capital on vegetable marketing is that possibly more efficient marketing arrangements are foregone in lieu of friendships and tribal ties, resulting in inefficiency and increased transaction costs for both parties. To prevent long term market inefficiency, the strength of informal networks can be employed to promote the formation of formal networks, inter-tribal transactions and a properly functioning institutional environment.