Observations of PSR 1133+16 at frequencies of 20 and 25 MHz were conducted for the first time nearly 20 years ago (Bruck and Ustimenko 1973), and during the course of this work, its interpulse emission (IPE) was discovered. Systematic investigations of this pulsar at frequencies of 17, 20 and 25 MHz have been conducted using the UTR-2 radio telescope over the interval between 1972 and 1988, and occasional additional studies at 30 and 40 MHz were carried out since 1981 using DKR-1000 radio telescope. The form of the main pulse was studied and IPE searched for and investigated. The sporadic IPE components were identified on the basis of their intensity, their dispersion measure, and their time and frequency repeatability, and in some cases were confirmed by observations at different observatories.