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High-pressure neutron-diffraction experiments on the pseudo-ternary compound NdAl[sub x]Ga[sub 2-x] revealed a pressure-induced isostructural phase transition for x = 1.00 and 1.08 above about 1.5 GPa at room temperature. Within its hexagonal AlB[sub 2] structure the compound changes its lattice ratio c/a discontinuously from 0.97 to 0.84 in analogy to chemical pressure for x > 1.12. Pressures up to 5.2 GPa did not result in a pure high-pressure phase but rather in a mixture of both phases. The intermetallic MN[sub 2] phases of the AlB[sub 2] structure are known to appear in two distinct groups with different c/a ratios. The observed isostructural transition is discussed within the framework of near-neighbor diagrams. [ABSTRACT FROM AUTHOR]