[en] To investigate a field-induced level crossing of the ground-state doublet in PrTr_2Zn_2_0 (Tr = Rh, Ir), we performed ultrasonic measurements in pulsed magnetic fields applied along the [110] and [001] directions and analyzed the results in the framework of the strain-susceptibility approach. Above 40 T for H∥ [110], we observed an elastic softening of the transverse modulus (C_1_1 - C_1_2)/2 corresponding to the ground-state doublet. In both compounds the softening is followed by a minimum at about 47 T at low temperatures. We predict the presence of a new field-induced phase boundary in PrTr_2Zn_2_0 at this field with two possible cases. The magnetic field of the minimum cannot be explained by only the quadrupole interaction. (author)