A new index of species abundance (ISA) is described that is calculated for individual species and encompasses numerical abundance and spatial distribution. Data for calculating theISAis arranged in a two-way table with species composing the rows and columns representing collection sites. The data of the index are ranks and the species in each column are ranked by numerical abundance, with average ranks used for tied scores. A value a is obtained by multiplying the number of zero cells in all columns for each row, byc. One is added to the single largest assigned rank in the columns to obtainc. The sum of ranks,Rjis the summation of assigned ranks in all columns for each row. TheISAis calculated with the formula,$\tt\ ISA = \frac{\text{a}+R_j}{\text{K}}$A formula is presented for astandardized ISA, giving indices between 0 and 1. An estimator of standard error for theISAis described along with an analysis of the components of theISAand a discussion of practical applications.