The Damaraland mole-rat Cryptomys damarensis exhibits anextreme reproductive division of labour. Reproduction in thecolony is restricted to a single breeding pair, resulting froma two-fold control: (i) a reduced pituitary synthesis and/orsecretion of luteinizing hormone leading to a block toovulation in non-reproductive females; and (ii) a stronginhibition to breeding with familar kin.Circulating basal concentrations of luteinizing hormone as wellas luteinizing hormone levels measured in response to a singleexogenous gonadotrophin releasing hormone challenge, weresignificantly lower in non-reproductive females in the presenceof the reproductive female than those in colonies lacking areproductive female. Urinary progesterone concentrations beforethe removal of the reproductive female were significantlyhigher in non-reproductives than the post removal values.Behavioural studies from sib-sib and non-sib pairings provideevidence for a strong incest avoidance, probably resulting froman inhibition of breeding with familiar colony members. A totalof four pairings of non-sibs resulted in copulatory activityand eventual conception. In contrast, four couples of sib-sibcombinations failed to produce any sexual activity oroffspring. Thus, suppression of reproduction in these non-reproductive, subterranean bathyergids is complicated by themasking effect of familiarity that prevents incest, in additionto the physiological inhibition of fertility in the presence ofthe reproductive female.