Abstract. Primary cultures of differentiated sheep thyroid were investigated to assess the effect of varying the media, sera, hormones and the initial cell number plated on the culture life span. Iodide uptake and follicular morphology were used as indices of differentiation.
It was found that the effect of variations in the type of medium and the concentration and type of serum used was very small. The addition of all the hormones used – insulin, hydrocortisone and thyrotrophic hormone – had a synergistic effect on the iodide trapping ability of the culture system. A cell number of approximately 1 × 106 cells per 25 cm2 flask was found to be optimum for the development of differentiation in the cultures.