Light, fluorescence and electron microscopy were used to analyse the structural properties of protoplasts obtained from established suspension culture of Solanum lycopersicoides Dun, composed of meristematic cell aggregates. Four types of protoplasts were distinguished immediately after isolation: (1) mononuclear; (2) polynuclear, (3) anuclear and (4) homogeneous protoplasts. Only mononuclear protoplasts were capable of complete cell wall regeneration and mitotic division. Other types of protoplasts were eliminated during culture. Three phases were distinguished in the developing protoplast culture: (1) the elimination phase during which protoplasts damaged during isolation underwent complete degradation; (2) a phase of intense division during which both mitotic cell division and amitotic nuclear division took place; and (3) a stabilization phase leading to the formation of suspension culture. The cell suspension culture obtained from protoplasts was capable of regenerating diploid plants.