Tissue cultures were initiated from root sections excised from 5∼7 day-old seedling, in 60 varieties including various ecospecies i.e. japonica, indica, japonica-iridica hybrids, and large grain varieties (assumed to be javanica type) in rice (Oryza sativa L.) on basal Murashige and Skoog's (1962) medium containing 3.0 mg/l 2, 4-dichlorophenoxyacetic acid (2, 4-D), 2.O g/l of casein hydrolysate, and 30 g/l sucrose. Cultures were maintained on the same medium with 2.O mg/l 2, 4-D. Plant regeneration was accomplished by subculturing for 2 to 3 passages to the same basal medium with 0.02mg/l 2, 4-D and 10mg/l kinetin. Remarkable variability in plant regeneration was observed among varieties tested. All the cultures of the japonica varieties had good capacity for regeneration, while some of the cultures of indica, japonica-indica hybrids, and large grain varieties were poor. It was observed that 11 of 28 cultures in japonica, 2 of 16 in indica, and 1 of 10 in large grain varieties had relatively high potential for regeneration at more than 30%. Besides normal plant regeneration, cultures showed various responses such as massive rooting without shoot formation, retention of green pigmented region without further development, and occurence of necrotic dead tissue. Two distinct types of plant regeneration were observed, one of which was organogenesis, and other was somatic embryogenesis. Most of the cultures from the indica varieties, Chyokoto and Gaiya Dhan Tosar, initiated plantlet through somatic embryogenesis.