HPPH-PDT enhances neutrophil infiltration into the treated tumour. Animals were treated with 0.6 μmol kg⁻¹ HPPH, followed 24 h later by 100 J cm⁻² of 665 nm light. Tumours were harvested at various times post-PDT and the infiltrating cell populations were analysed by flow cytometry as described in Materials and Methods. Samples were collected from control animals (no treatment, HPPH alone) at 6 h ‘post-PDT’. Results are reported as the percentage of total cells present in the tumour that are CD45⁺ and Gr-1⁺. A minimum of three mice were analysed at each time point. Error bars represent the s.e.