Hidden capital exists whenever the accounting measure of a firm's net worth diverges from its economic value. Such unbooked capital has on-balance-sheet and off-balance-sheet sources. This paper develops a model to estimate both forms of hidden capital and to test hypotheses about their determinants. In effect, the analysis expands the two-index model by endogenizing the market and interest-rate sensitivities of any stock and decomposing each sensitivity into on-balance-sheet and off-balance-sheet elements. For a sample of banks during 1975–1985, the model finds considerable variation in both forms of hidden capital.