Zn K-edge EXAFS data of the matrix metalloproteinase (MMP) stromelysin-1 were obtained in both its latent proenzyme and mature active forms. The Fourier-filtered (back-transform 0.7–2.3 Å) χk3 spectrum of mature stromelysin was satisfactorily simulated with 4 N/O scatterers per Zn at 2.01 Å, while similar fits for prostromelysin were judged unacceptable because of unreasonable Debye–Waller factors or significantly larger residuals of the fits. For prostromelysin, excellent fits were obtained with the introduction of a sulfur scatterer at 2.25 Å. These data provide the first direct evidence for the coordination of zinc by the sole cysteine in the N-terminal domain of prostromelysin and confirm that the cysteine is lost upon activation. These results provide support for a “cysteine switch” structural model for MMP proenzymes that suggests the interaction of the conserved propeptide cysteine with zinc is present in the latent form. Examination of the Zn–S bond length and outer shell carbon contributions suggests that the 2 g-atoms of zinc recently shown to be present in stromelysin (Salowe, S. P., et al. Biochemistry 1992, 31, 4535–4540) reside in independent zinc sites.