Because multiple simultaneous reflection of x rays is very sensitive to lattice deformation, the six-beam, (000) (006) (22̄4) (22̄2) (2̄24) (2̄22) multiple reflection was used to record simultaneously the information about the lattice mismatch of [001] InGaAsP materials using a divergent x-ray source. The lattice mismatches in directions parallel and perpendicular to [001], determined from a single divergent-beam photograph, increase as the As concentration in liquid composition Xl As increases. The procedure was used without difficulty for X l Ga as low as 0.0007 and Xl As in the range 0.006-0.01.379819821