Perovskite manganese oxide materials known for the phenomenon of colossal magnetoresistance often exhibit anomalously large 1/f noise and large, temperature-dependent ferromagnetic resonance (FMR) linewidths. We show that in epitaxial films, these anomalies are very sensitive to oxygen partial pressure during film growth and to postdeposition thermal processing in oxygen, suggesting that oxygen stoichiometry plays a key role. We find that the temperature coefficient of resistance (TCR) at the metal–insulator transition increases and the FMR linewidth decreases as we increase the oxygen partial pressure during growth. Postdeposition heat treatment in oxygen leads to further increase in TCR and decrease in FMR linewidth, accompanied by a dramatic reduction in 1/f noise magnitudes. © 1998 American Institute of Physics.