Four fluorescent whitening agents (FWAs) were tested for mutagenic activity after oral administration in the following three different mammalian test systems: (1) Dominant lethal test in the male mouse; (2) Cytogenetic studies on metaphase chromosomes from the bone marrow of the Chinese hamster; (3) Nucleus anomaly test in somatic interphase cells (bone marrow) of the Chinese hamster. These investigations yielded no evidence of dominant lethal effects of any of the four compounds on the progeny of male mice. Furthermore, the data obtained from chromosome analyses and the nucleus anomaly test revealed no effects at all. Thus, the results obtained in all these tests gave no indication of mutagenic activity after the administration of these compounds in dosages up to approximately 1/3 or the LD50.