This paper reports the results of two studies of the readability of FORTRAN programs, i.e., the ease with which a programmer can read and analyze programs already written, particularly in the processes of maintenance and debugging. In the first study, low-level characteristics of 202 FORTRAN programs stored on the general-use UNIX systems at Bell Telephone Laboratories were analyzed to see how strongly they correlated with the number of lines of code in each program, i.e., the number of executable statements. Three measures were found to be relatively independent of lines of code: (1) statement length, defined as the total number of operators and operands divided by the number of executable statements; (2) module redundancy, defined as the degree to which the program uses subroutines and functions properly; and (3) average active variables, defined as the average number of variables that must be kept in mind while reading the program. The effects of these three variables on readability were assessed in the second study. In two different surveys of experienced programmers, they accounted for 66 percent and 72 percent of the variance in rated readability. The results must be considered tentative because the sample sizes involved are small. A list of seven references is provided. (Author/ESR)