38 differences in temperature on maximum stimulation with the various mitogens. Cells stimulated with PHA (0.1 yl) and Con A (50 yg) re sponded well at 32C (p < 0.01) and very poorly, if at all, at 22C (p > 0.1), whereas LPS (1 yg) responsiveness was higher at 22C (p < 0.01). There was, however, a significant response (p < 0.05) to LPS (10 yg) in 32C incubated cultures which was reproducible. Fifty micrograms of LPS (not shown) were not stimulatory (stimulation indices _< 1) at either temperature. The temperature effects described above were found in ten experi ments with the only major differences being the magnitude of the re sponses. These differences may have been due to differences in the serum supplement pools used as discussed previously. To summarize the results, optimal mitogen doses at 32C were 0.1 yl, 50 yg, and 10 yg for PHA, Con A, and LPS respectively and. 1.0 yg of LPS at 22C. PHA and Con A responses were greater at 32C than 22C and LPS responsiveness was greater at 22C than 32C. Optimal culture times were 5-7 days for all mitogens with the exception of 10 yg of LPS at 32C where some variations were noted. Limited experiments with spleen, blood, and thymus lymphocytes indi cated that all were stimulated by PHA, Con A, and LPS. The mitogenic responses of thymus lymphocytes are presented in Table 5 to demonstrate that the temperature effects on mitogenic stimulations were also observed with cells from this tissue and thus were not limited to anterior kidney lymphocytes. Mixed Lymphocyte Cultures Lymphocytes from anterior kidneys of different bluegills were tested for their ability to respond in two-way mixed lymphocyte cultures