[en] Fixed boundary n = 1 MHD instabilities are studied computationally as a function of diamagnetism (β/sub pol/) and current profile in elongated toroidal equilibria (1 < b/a less than or equal to 4). It is found that even slightly diamagnetic plasmas with broad current profile and a highly elongated cross section are subject to a ballooning instability for q-values well above unity at the magnetic axis. A peaked current profile in a mildly diamagnetic plasma decreases the elongation of the inner flux surfaces and reduces the marginal q-value by suppressing ballooning modes. The maximum stable volume-averaged beta is achieved with a broad current profile and either a paramagnetic plasma (β/sub pol/ < 1) with a highly elongated cross section (b/a > 2) or a diamagnetic plasma (β/sub pol/ > 1) with only a mildly elongated cross section