Using ultrasonic methods, the complete polycrystalline elastic constants of four Fe-Cr-Ni-Mn alloys were measured. Combining these results with those reported previously for five similar alloys, the focus was on the alloying effects of chromium, nickel, and manganese. The alloys contained 16 to 23 at % chromium, 7 to 28 at % nickel, and 0 to 13 at % manganese. Only manganese produced regular effects, consistent with volume changes. Both chromium and nickel produced surprising increases in the bulk modulus and equally surprising decreases in the shear modulus. It is hypothesized that changing the bonding electrons from a d-character to an s-character explains such irregularities. The measurements were examined with Ducastelle’s model, which contains two terms : a band-structure term and a repulsive-energy term.