Siliconized, glass micropipets whose tips were filled with oil were used to obtain small (<100 nl) liquid samples from perilymphatic and endolymphatic regions of the inner ears of anesthetized animals: 3 cats, 19 alligator lizards (Gerrhonotus multicarinatus), and 8 skates (Raja erinacea). Samples of cerebrospinal fluid and seawater were also obtained for skates. Electron probe microanalysis was used to measure the concentrations of the following elements in each sample: K, Na, Cl, Ca, Mg, P, S. The Na and K concentrations in cat perilymph (Fig. 1 and Table 2) agree with previous estimates (Table 4) while endolymph samples show relatively low Na and high K concentrations. From a comparison of our results with previous work (Table 3), we infer that contamination of endolymph samples with perilymph is relatively low in our study, and that no large species difference in endolymph content is indicated by present data available for mammals. Our results show that Cl concentration is higher and Ca and Mg concentrations are lower in endolymph than in perilymph. The composition of perilymph in cats and alligator lizards is roughly the same (Figs. 1 and 2, Table 2). Uncontaminated endolymph samples in lizards were apparently difficult to obtain, although the compositions of a few samples suggest that endolymph K concentration is high and Na concentration is low. In skates the concentration of Na is nearly the same in the two inner ear lymphs (Fig. 3 and Table 2), in contrast to the roughly hundredfold ratio of perilymph to endolymph Na concentrations found in the higher vertebrates. The element composition of perilymph is correlated with the composition of seawater in which the skates were kept, whereas the endolymph composition shows no such correlation.