Quantitative intensity measurements of several forbidden transitions of Fe II and Fe III in the spectrum of the type Ia supernova 1991T at age 1 yr are presented. The two species account for virtually the entire observed optical and near-infrared spectrum. These data are fundamental to tests of the explosion models of supernovae, and allow a direct determination of the mass of 56 Ni produced. The line intensities support models that require most of the white dwarf precursor to be converted to 56 Ni