A readability formula for elementary Spanish instructional materials was developed by building on previous research, particularly in regard to the application of the Fry readability graph to Spanish language materials. The study began with the selection of average sentence length and number of syllables per 100 words as independent variables. Sample 100-word passages were selected from each grade level of ten different basal reader series used in the United States, Latin America, and Spain. The mean and standard deviation for average sentence length and number of syllables per passage were tabulated, and multiple regression analyses were performed for each series. Grade level was the dependent variable. A formula was derived from the analyses, and a readability graph was generated by computer to eliminate the computation and simplify use of the procedure. It is suggested that the formula and graph provide a procedure as convenient for Spanish as the Fry graph is for English, and that it can serve as a guide for writing elementary level instructional materials in Spanish and for teachers in selecting materials. Several tables detailing the data analysis are included in the text. (MSE)