Growth of 3 laboratory populations ofBlattella germanica(L.) was followed by monthly censuses. Two of them, Populations A and B, originated from 5 wild type ♀, 3 wild type ♂ and 6 ♂ heterozygous for T(9;11). The 3rd was a control started with 5 pairs of wild type. T(9;11) male nymphs were released repeatedly into Pop. B so as to maintain about 2–3 T/+ ♂:1 +/+ ♂. Releases were timed to match oncoming groups of female nymphs in age.The single introduction of T(9;11) into Pop. A held the F1and an oncoming F2group to ca. ½ the size of comparable groups in the control. This experiment was terminated after 4 months. Repeated introductions markedly retarded, but did not prevent, the growth of Pop. B throughout a 6-month period. Analyses of oothecae for mating types indicated good competitiveness of T(9;11) males. About 4% of the matings in Pop. B were +/+ × +/+. The others were either T/+ × +/+ (semisterile) or T/+ × T/+ (sterile). The translocation was successfully incorporated into the population by careful timing of male releases.An analysis is presented as to the origin and growth of nymphal groups present at successive censuses. Population size replacement, mortality, carrying capacity of the breeder jar and other data useful to future population studies are discussed.