Measurements of the magnetization versus magnetic field for temperatures just above the superconducting transition in a high-T C underdoped cuprate (La 1.9 Sr 0.1 CuO 4 ) and in a low-T C Pb 55 In 45 alloy are presented. At low-field amplitudes (H≲10 −2 H C2 (0), where H C2 (0) is the corresponding upper critical field extrapolated to T=0K) the magnetization of both types of samples presents an anomalous diamagnetic contribution [much larger than the one predicted by the Gaussian–Ginzburg–Landau (GGL) theory for the thermal fluctuations] that disappears at higher magnetic fields. We show that it may be explained at a quantitative level, and consistently with the GGL approach, in terms of uniformly distributed T C -inhomogeneities associated to spatial chemical variations around the mean composition.