This paper reports a study of three cultivars of rice (Oryza sativa,L.), namely cv IAC-435, cv IAC-120, and cv IAC-68 cultivated as main crops in the lowland conditions of the State of São Paulo, Brazil. Observations on these cultivars were made in 1969/70 and 1970/71 fiscal years at the Campinas, Mococa and Pindamonhangaba Experiment Stations of the Instituto Agronômico of the State of São Paulo. The results obtained in this study permit a correct identification of the cultivars, and also establish proper procedures to study other cultivars of rice, with special emphasis to their morphological characteristics related with seed production.