Rat parotid, submaxillary and sublingual salivas, collected directly from the respective gland ducts following a single stimulatory dose of pilocarpine, show widely divergent Na and K concentrations at high flow rates. Parotid secretion shows high Na and low K levels; submaxillary, low Na and high K; sublingual has intermediate levels of both electrolytes. Changes in flow rate and duration of secretion modify Na-K balance. With decreasing flow rate and increasing duration of flow, Na level of parotid secretion decreases, whereas Na of submaxillary increases before decreasing. Concurrently, K in these secretions first shows a transient elevation followed by a decrease and subsequent increase. Parotid saliva is usually isotonic or slightly hypertonic to serum at high flow rates; submaxillary and sublingual secretions are generally hypotonic at all flow rates. Some correlation between electrolyte levels of gland and secretion seems apparent.