The following general conclusions can be made concerning the use of tissue culture for assaying the effects of mineral elements from simulated lunar soil or other mineral samples: The method used here is a very sensitive one for showing that soluble materials are reaching the tissue explant. The effects found (inhibiting) are very probably caused by excess toxic materials or competition of non-essential elements with essential elements rather than pH changes because previously pH has been found- to have relatively little effect over a wide range. Any stimulatory effect of the simulated lunar soil will probably appear at concentrations below those used in these experiments. If this is the case, the method is much less wasteful of mineral materials than methods in which pre-grown callus is treated with mineral materials. Measurements of uptake of minerals will be difficult in this system because of the relatively small growth obtainable from the tissue and also because of the apparently large background of minerals contributed by the purified agar.