Recent observational studies on solar flares made by solar radio groups in Japan during the period around the maximum of Cycle 21 are briefly reviewed. Much attention is paid especially to comparison studies of microwave observations with hard X-ray and 7-ray observations. Three solar radio groups in Japan, namely the Toyokawa, Nobeyama, and Nagoya groups, have accumulated flare observations during the period around the maximum of Cycle 21. Collaborating together, the three groups had wide spectral coverage of single-frequency observations in the microwave to millimeter-wave ranges (at present, 1, 2, 3.75, and 9.4 GHz at Toyokawa, and 17, 35, and 80 GHz at Nobeyama). The temporal resolutions of these single-frequency observations are fractions of a second. In adition they have been using 3.75 and 9.4 GHz radioheliographs at Toyokawa, a 17 GHz interferometer at Nobeyama, and a 35 GHz interferometer at Nagoya. (The 35 GHz interferometer ceased observations in 1983.) Although the spatial resolutions of these instruments are about 30 %nd much inferior to that of the Very Large Array, their wide fields of view enable us to observe many flares with temporal resolutions between about one second and a few tens of seconds.
Thanks to the advantages mentioned above, many observational studies have been done in Cycle 21. Much attention has been paid to clarify the acceleration and confinement of particles during flares. Detailed comparisons have been made of microwave observations with hard X-ray and 7-ray observations from the ~Hinotori' and the SMM spacecraft. A brief review follows: