This paper is a review of the most notable experiments conducted at IPP RAS in cooperation with IRE RAS and dedicated to influences of millimeter wavelength irradiation, temperature T, and magnetic field B on the conductivity of superconductor—insulator—normal metal—insulator—superconductor (SINIS) tunnel structures at temperatures T ≪ T_C and at low bias voltages when a single-electron current is comparable or less than the two-electrons Andreev current. It was determined, that under irradiation with photons energy ħω ≫ kT, the electron subsystem in a normal metal does not reach equilibrium. Under pulsed irradiation, the time constant of NIS structures as a radiation detector was estimated at several microseconds. The effect of a magnetic field on the single-electron and Andreev conductivity of NIS was investigated.