Novel in-beam spectroscopic methods utilising the recoil-gating and recoil-decay- tagging techniques were employed for the spectroscopy of very heavy elements 252,253,254No and 255Lr. In-beam γ-ray spectroscopy of these nuclei is based on the use of germanium detector arrays in conjunction with the gas-filled recoil separator RITU. The major part of this work was to design the collinear SACRED electron spectrometer to be used in conjunction with RITU. For the first time it was possible to obtain recoil-gated conversion-electron spectra. The ground-state bands in the even-even 252,254 No nuclei were observed. Global systematics and the extrapolated energy of the lowest 2+ state were used to deduce the deformation parameter β2 for these nuclei. The studies of odd-A 253No and 255Lr nuclei indicated that the de-excitations in these nuclei mainly proceed via cascades of Ml-transitions.