The carotenoid composition of cysts of seven species of fairy shrimps (Anostraca) was studied using high-performance liquid chromatography. Canthaxanthin was detected as the major pigment, but an important and often predominant fraction of it occurred in the cis-configuration, which is consistent with previous findings in Artemia cysts. Cis-canthaxanthin rapidly disappeared in nauplii of Thamnocephalus platyurus through conversion to all-trans-canthaxanthin and was preferably localized in the abdominal section carrying the genital segment of females, unlike in mature male animals. In contrast, the intense orange-red colour of the thoracopods and the cercopods in both sexes was only due to all-trans-canthaxanthin.