We have studied the critical region of RbMnF3 (T N=83°K) using specific heat, x-ray, and strain-gauge measurements. Because RbMnF3 so closely resembles an ideal Heisenberg antiferromagnet, experimental results may be especially relevant to theoretical predictions. The specific heat is found to diverge logarithmically over three decades for T<TN, but only over two decades for T<T N. No distortion from cubic symmetry is detectable in the range 20°to 300°K. Finally a remarkably small thermal expansion anomaly is found in a narrow region near TN. © 1966 The American Institute of Physics.