Perforin levels in the supernatant were determined at median culture periods of 41 (range 33–62) and 48 (range 36–74) days for TIL from melanomas and colorectal carcinomas, respectively, and were elevated in both tumour types, especially in TIL from colorectal carcinomas (median MESF 22,118; range 10 000–81 000). The gene discussed is PRF1; the disease is colorectal carcinoma.