We present results of the observations of 17 molecular clouds associated with bright FIR sources in the NH_3_ (1, 1) and (2, 2) lines with the 100-m radio telescope in Effelsberg. The lines were detected in 11 clouds and 10 of them have been mapped in these lines. The kinetic temperatures, sizes, masses and mean densities of the ammonia cores have been derived. For most of the detected clouds the masses derived under the assumption of a relative ammonia abundance of {chi}(NH_3_)=3x10^-8^ are close to virial masses. However, in S 88 B the ratio M/M_vir_ is only ~0.1 and in a few other cases this ratio is significantly lower than unity which may indicate ammonia underabundance. Almost all objects with the signs of underabundance are among the most luminous IR sources in our sample. Most of the mapped cores are elongated with noticeable velocity gradients along the major axis. The most prominent example is S 255. S 87 has a two-component structure with 2 distinct velocity components which overlap partly spatially. In about half of the mapped sources the NH_3_ line widths increase near the peaks of the ammonia emission. The kinetic temperatures are centrally peaked. They reach 20-28K in the centre and drop to 15-20K at the edges of the ammonia emitting regions. In S 76 E a weak extended emission in the (1, 1) line at the velocity blue-shifted by ~5km/s relative to the core emission was detected. Hyperfine intensity anomalies in the (1, 1) transition were found in S 199 in addition to the known case of these anomalies in S 87.