This article is a highlight of the paper by Lazic et al. in this issue of Photochemistry and Photobiology, https://doi.org/10.1111/php.12767. It describes the validation of osmium coordination complexes as photosensitizers for photodynamic therapy, with very promising in vivo results that demonstrate radical improvements in survival following irradiation with visible (635 nm) or near-IR (NIR; 808 nm) light. An unusual feature in the study is that the different complexes exhibit disparate photophysical and photobiological characteristics, despite sharing common structural motifs. These findings raise hopes for the development of novel photosensitizers that overcome the limitations of current commercially available systems for PDT, but also raise questions regarding the most efficacious biological mechanisms of action for this treatment modality.