Large intracellular vacuoles, >4 microm in diameter and either round or oval-shaped, were observed infrequently in Dictyostelium discoideum amoebae of axenically-grown strain AX2 (only 1 in 10(6)-10(8)cells). These previously unreported single or multiple 'giant' vacuoles were more common, however, in newly germinated KAX3 cells (0.55% of the population) and AT-K(neg), a strain that lacks an es...