The laboratory stand with the squid-based gradiometer was developed and tested in experimental studies of magnetic nanoparticles used in medicine. Two versions of the cryogenic probe were tested in investigations, the first of which included an additional XYZ squid-based magnetometer for "electronic" balancing of the input signal gradiometer in a uniform magnetic field. The second probe contained in its design movable trimmers with superconducting plates located in the area of the input loops of the gradiometer for its mechanical balancing. Both cryogenic probes demonstrated stable operation of the squid-based gradiometer at usual laboratory conditions without additional magnetic shielding. The stand was used to study the magnetization of aqueous suspensions of magnetite nanoparticles in various concentrations, which was induced using an uniform magnetic field with an amplitude of up to 15 milliTesla, created by a special system of Helmholtz coils at a frequency range of 4-12 Hz in the vertical and horizontal directions. The magnetic signals of nanoparticles were recorded using a second-order axial gradiometer in a «2:4:2» configuration with an input loop diameter of 8 mm and a base length of 29 mm. The experimental studies of the magnetization of aqueous suspensions of magnetite nanoparticles were aimed at estimating the limiting resolution of the SQUID gradiometer by the number of detected magnetic nanoparticles. The possibility of registering a magnetic signal from about 6 × 109 MNPs of magnetite 6 nm in size in a volume of 1 ml from a distance of about 20 mm from the receiving coils of the gradiometer was demonstrated. Dry liver extracts of small animals containing MNPs were also used as objects of study. Directions of further improvement the used instrumental elements and methods of magnetic measurements for increasing the sensitivity of squid-based gradiometers in experiments with MNPs are determined.