Data processing for an improved securities brokerage/cash management system supervises, implements and coordinates a margin securities brokerage account; participation in one or more short term money market or comparable funds; and subscriber-initiated use of electronically responsive subscriber identity credit/debit media and/or checking systems. Subscriber expenditures, effected as by "charge card" use, check and/or cash advance are applied on a hierarchal basis, seriatim, against the subscriber's free credit balance, short term investment and the lendable equity in his securities account. On a periodic basis, e.g., daily, received card charges, check, securities and deposit transactions for the ensemble of account participants are verified and employed to compute an updated credit limit for each subscriber. The transactional data is reviewed against predetermined norms to detect abuses such as check kiting. The short term investment position of each account is modified as necessary to permit money market or comparable earned yields on the account free credit cash balance.