1. A method for producing a standard low-fluoride diet from a green alga and yeast is described. Chlorella pyrenoidosa was grown in a culture medium prepared with distilled water and analytical grade chemical salts. The spent culture medium from the alga culture was reclaimed and replenished with salts and sucrose for the production of yeast, Saccharomyces cerevisiae.

2. The single-cell organisms were separated by centrifugation from their culture media and the dried cells were blended with sucrose, maize oil, cellulose and a salt mix to produce diet pellets for rats and mice.

3. The diet was readily accepted as food by rats and mice and it was found to contain 100–300 μg fluoride/kg dry weight. Two generations of rats and four generations of mice were bred on this diet.

4. The use of hydroxyapatite to reduce the fluoride content of the chemicals used in the production of the alga and yeast biomass was investigated. Diet pellets prepared with this biomass contained 45–60 μg fluoride/kg dry weight.

1. Rats were fed for 14 d on diets containing 50, 150 or 250 g/kg casein as the protein source. The daily excretion of Nt-methylhistidine (His(τMe)), a non-re-utilized amino acid, was determined.

2. His(τMe) excretion/100 g body-weight appeared to be unaffected by increasing the concentration of dietary protein from 150 to 250 g/kg. Assuming no change in the proportion of muscle in the animals these results are indicative of no change in myofibrillar protein catabolic rate. The excretion rate/100 g body-weight of the animal given 50 g/kg casein was lower than the other two treatments, especially towards the end of the 14 d treatment period. Thus at this time the myofibrillar-protein catabolic rate was lower than in the animals fed on the higher protein diet.

3. In the animals fed on the high protein diet there was a tendency for this (τMe) excretion rate/100 g body-weight to increase with age.

4. Nitrogen balance and creatinine excretion results are also presented.