Empirical studies of covered interest arbitrage suggest that the parity condition is not always satisfied and thus implying unexploited profit opportunities. This paper provides a procedure for estimating transaction costs in the markets for foreign exchange and for securities. Allowance for these costs accounts for most of the apparent profit opportunities. It is shown that in addition to transaction costs, demand and supply elasticities in the various markets and lags in executing arbitrage can account for all of the apparent profit opportunities. It is concluded that empirical data are consistent with the interest parity theory and that covered interest arbitrage does not entail unexploited profit opportunities.