Analysis of single strand conformation polymorphism (SSCP) of an amplicon (123 bp) obtained by polymerase chain reaction (PCR) of the mitochondrial cytochrome b gene was used to identify the fish species in canned tuna. Single-stranded DNA (ssDNA) was separated by polyacrylamide gel electrophoresis, and visualised by silver staining. The reliability of the method was tested by a collaborative study in which eight European laboratories participated. Seven unknown samples (five from individual species and two mixtures of two tuna species) of canned tuna had to be identified by comparison with reference material. From a total of 72 cases, 65 (90.3%) were assigned correctly. Intra-species variability of SSCIP patterns was found in the case of Katsuwonus pelamis and Sarda sarda. As specimens from various fishing grounds gave two or three different patterns of ssDNA, the possibility of some variability of the DNA patterns has to be considered in SSCP analysis of these species. (C) 1998 Elsevier Science Ltd. All rights reserved