To establish a parameter for zinc status that is independent of the occurrence of infection, we studied the effects of low dietary zinc and endotoxin in weaning rats 21 d after65Zn intubation. We monitored aspects of zinc status (tissue zinc content,65Zn distribution, and specific65Zn activity in tissue) and65Zn metabolism (absorption, excretion, and biologic half-life), as well as weight gain, feed conversion, and dietary zinc use. The low zinc diet iuduced classical deficiency with losses of bone zinc, resulting in lower content (7.4 versus 19.6 μmol) and higher specact (17versus8 kBq/μmol). Other tissue-specific and plasma-specifie activities were also higher (overall, 20versus8 kBq/μmol; plasma, 8versuskBq/μmol). Endotoxin caused lower total-plasma zinc (0.04versus0.05/μmol) but did not affect spec act (4 kBq/μmol): combined endotoxin and low-zinc diet caused low total-plasma zinc (0.01 μmol) and high spec act, as did the low-zinc diet alone (12 kBq/μmol). We conclude that plasma-spec act (or stable isotope enrichment) can serve as an index for nutritional zinc status during recurrent infection. (Pediatr Res28: 332–335,1990)