The gamma-ray transitions from the states populated in ⁵⁶Fe, ⁷⁵As and ¹⁵⁶Gd by the decay of ⁵⁶Co, ⁷⁵Se and ¹⁵⁶Eu were investigated using six Ge(Li) detectors and an intrinsic Ge detector. Coincidence studies were undertaken with a Dual-Parameter Energy-Time Spectrometer employing a fast-plastic scintillator detector and two large volume Ge(Li) detectors. The energies and intensities of measured gamma-rays were determined. The lifetime of energy levels in the n sec. range belonging to ⁷⁵As and ¹⁵⁶Gd were measured. The level schemes were constructed; log ft values, transition multipolarities, spins and parities were deduced. Different shell-model calculations were discussed and compared with experimental results.