The removal method of population estimation was applied to populations ofBlattella germanica(Dictyoptera: Blattellidae) aboard two ships. A preponderance of adult females was collected from both ships. A low frequency of females with oothecae indicated that many were senescent or were delaying reproduction. Instar determination was made by head capsule measurements. Female nymphs appeared to have six instars, whereas males had only five. Structure of the two ships' populations indicated that cockroaches were at near carrying capacity on the larger vessel, whereas the population on the smaller ship was less dense.Calculation of the removal method estimators for the two populations indicated that adult females are more resistant to capture than nymphs or adult males. Significant bias in estimation of population size resulted if this factor was not accounted for. Both precollection and residual population size was estimated with coefficients of variation of 3 to 13%.