Experimental results are presented for a simplified version of Hart s(1995) theory of the firm. Theory predicts that investment levels remain constant when investors no-trade pay-offs increase, if these pay-offs are threat points. While they may decrease when no-trade pay-offs are outside options. Our results support these predictions in a relative sense. Average investment levels exceed the predicted level. Actual investment behaviour is consistent with the outcomes of the bargaining stage. The play of the game is supported by a reciprocity mechanism in which non-investors consider higher investment levels as fair behaviour which deserves a reward. Investors anticipate this.