Sarcolemmal vesicles prepared from rat heart exhibited ATP-dependent uptake of S-(2,4-dinitrophenyl)glutathione (DNP-SG), which obeyed Michaelis-Menten kinetics with an apparent Km of 21 /zM for DNP-SG and a Vmax of 0.27 nmol-I0 min -1 •mg protein -~ . Several model glutathione S-conjugates inhibited DNP-SG uptake, but leukotriene C 4 inhibited uptake much more significantly even at lower concentrations (competitive inhibition, Ki = 1.5/zM). However, leukotrienes D 4 and E 4, which lack the ¥-glutamyl moiety, were less effective. The results suggest that the ATP-dependent transport system has a high affinity for leukotriene C4, and may be responsible for the translocation of this compound.