Abstract 1. 1. The spacing patterns of females of Drosophila paramelanica hanging suspended from a moist filter paper were determined. 2. 2. The females were relatively uniformly spaced. Within limits the mean distance between adjacent flies became more uniform as the population density increased from low levels. At higher densities the spacing pattern of the flies was relatively constant. 3. 3. The number of flies capable of remaining on the filter paper was limited. 4. 4. This limitation of the number of flies and the occurrence of the uniform spacing pattern of the flies are attributable to avoidance reactions made by flies when within 5 mm. of each other.