['Preliminary studies have suggested that photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) can improve psoriasis and mycosis fungoides, two diseases where normal or malignant T cells play a central role.', 'To determine if ALA-PDT induces apoptosis and caspase activation in Jurkat cells, a malignant T-cell line.', 'Jurkat cells were incubated with ALA in the presence of [14C]-thymidine followed by red light exposure. DNA fragmentation was measured 24 hours later with a DNA elution assay. The influence on DNA fragmentation of ALA concentration, time between ALA addition and light exposure, as well as light fluence were studied. The occurrence of oligonucleosome-sized DNA fragmentation was also studied with DNA electrophoresis. Caspase-3-like activity was monitored by measuring Ac-DEVD-AMC hydrolysis.', 'DNA fragmentation as high as 88% was observed 24 hours after ALA-PDT. The percentage of DNA fragmentation increased with increasing doses of ALA, red light fluence, as well as longer incubation time with ALA. DNA fragmentation was observed as early as 3 hours after ALA-PDT. The presence of apoptosis after ALA-PDT was confirmed by DNA electrophoresis. An increase in caspase-3-like activities was detected following ALA-PDT.'] Does photodynamic therapy with 5-aminolevulinic acid induce apoptosis and caspase activation in malignant T cells?