Microtubules (MTs) have an important role in plant morphogenesis because they participate in regulating cell-shape and determining the plane and site of cell division. As cells proceed through the cycle of growth and division, the MTs undergo a series of changes taking on a variety of different assemblies. In higher plants the MTs are organized cortically during interphase, as preprophase bands (PPBs) and perinuclear microtubules before or during prophase, as mitotic spindles during metaphase and anaphase, and as phragmoplasts during telophase. As microtubules are polymers of highly conserved proteins which form more or less standard substructures, it is believed that their cellular patterns are regulated spatially and temporally by MT nucleating-sites which are to a large extent under genetic control. Spatial control can be further modulated at the subcellular level by many factors including calmodulin, Ca2+ and Mg2+ concentration and MT-associating proteins. Furthermore, MT organization can be affected by intercellular factors acting across the cell wall and through plasmodesmata (molecular, hormonal, ionic and electrical gradients) and by environmental factors (temperature, light, gravity, pressure) (see reviews Gunning and Hardham 1982; Lloyd 1987; Derksen et al. 1990). The main advantage of studying the MT organization in protoplasts is that the intercellular influences are eliminated and the environment can be controlled. Extracellular conditions can be modified systematically to study chemical and physical effects on MT organization. In addition, the absence of the cell wall removes another stratum of possible controls as very little is known of the MT-plasma membrane-cell wall associations. The influence of the cell wall on MT stability or organization can be studied by the changes occurring after it is removed. The role of cortical MTs on microfibril orientation can be studied in the absence of influence from the old wall. This review of MT organization in protoplasts is restricted to higher-plant species.