Abstract Within the framework of the study of the unusual behaviour of relativistic secondary particles formed in the interaction of 72 GeV 40 Ar within a 1 cm thick Cu target, the wide-angle emission of heavy fragments has been studied with CR-39 SSNTD. Within the laboratory-frame forward angular interval θ, with 5° < θ < 43°, we observed such heavy fragments with a frequency F = (0.2 ± 0.1)%, expressed as a fraction of the total primary Ar flux. Evidence is presented that these fragments are possibly ‘projectile fragments’ (PFs) within the charge range 6 ≤ Z < 18, and that they have relativistic energies. No attempt is made to interpret this possibly ‘new’ phenomenon. However, it is pointed out that these ‘wide-angle emitted’ heavy fragments cannot be related to any ‘unusual’ behaviour (observed at wide angles) by projectile fragments in other experiments, provided that these fragments have ‘normal’ reaction cross-sections.