Ventilation (V) increases lung lymph flow (Q_L) but the separate effects of tidal volume (V_T) and frequency (f) and the role of ventilation-induced changes in edema formation are poorly understood. An isolated, in situ, sheep lung preparation was used to examine these effects. In 8 sheep with f = 10 min^-1, results obtained during 30 min periods with V_T = 5 or 20 ml^.kg^-1 were compared to values obtained during bracketed 30 min control periods (V_T = 12.5 ml^.kg^-1). Eight other sheep with constant V_T (12.5 ml^.kg^-1) were studied at f = 5 or 20 min^-1 and compared to f = 10 min^-1. Three additional groups of 6 sheep were perfused for 100 min with control V (10 ml^.kg^-1, 10 min^-1). V_T was then kept constant or changed to 20 or 3 ml^.kg^-1 during a second 100 min period. Increases in V_T or f increased Q_L and vice-versa without corresponding effects on the rate of edema formation. For the same change in V, changing V_T had a greater effect on Q_L than changing f. The Q_L caused by an increase in V_T was significantly greater after the accumulation of interstitial edema. The Q_L caused by a sustained increase in V_T was transient and did not correlate with the rate of edema formation suggesting that V altered Q_L through direct mechanical effects on edema-filled compartments and lymphatic vessels rather than through V-induced changes in fluid filtration.