We present our search program for substellar companions using high-precisionrelative astronomy. Due to its orbital motion around the star, an unseensubstellar companion would produce a periodic “wobble” ofthe host star, which is the astrometric signal of the unseen companion. Bymeasuring the separation between the components of stellar double and triplesystems, we want to measure this astrometric signal of a possible unseencompanion indirectly as a relative and periodic change of these separations.Using a new observation mode (the “cube-mode”) where theframes were directly saved in cubes with nearly no loss of time during thereadout, an adaptive optics system to correct for atmospheric noise and aninfrared narrow band filter in the near infrared to suppress differentialchromatic refraction (DCR) effects we achieve for our first target (the doublestar HD 19994) a relative precision for the separation measurements of about100. . . 150μas per epoch. To reach a precision in the μas-regime, we use a statistical approach. We takeseveral thousand frames per target and epoche and after a verification of aGaussian distribution the measurement precision can be calculated as thestandard deviation of our measurements divided by the square root of the numberof Gaussian distributed measurements. Our first observed target is the stellarbinary HD 19994 A & B, where the A component has a known radialvelocity planet candidate.