Mark and recapture methods were used to estimate populations of American cockroaches, Periplenata americana (Linnaeus), and brown-banded cockroaches, Supella supellectilium (Serville) inhabiting various rooms in the Science Hall, Iowa State University. These methods also permitted estimates of sex ratios, length-frequencies, movement, and activity patterns. Food appeared to be the limiting factor in determining size of cockroach populations. Males outnumbered females in both species with total sex ratios being.8 and.6 for brown-banded and American cockroaches, respectively. Most of the American cockroaches caught were over 28.0 mm. with the 36.1 - 40.0 mm. class being the largest. The brown-banded cockroach catch contained two large length classes, 2.5 - 4.0 mm. and 12.5 - 14.0 mm., suggesting two major age classes. Room-to-room movement of cockroaches was limited, and over 93 percent of the catch occurred during the dark hours
