Owing to their unique optical properties, gold nanoparticles find a wide range of applications in biomedicine, including nonlinear microscopy, single molecule sensing, DNA sequencing and targeted therapy. Illuminated by femtosecond pulses of high peak intensities at their plasmonic resonance, gold nanoparticles can strongly influence their close environment by the induction of various thermal, acoustic and ionization processes. This talk will present recent results in our attempt to control the fate of malignant cells using highly localized manipulations on a nanometric scale. We show that cells which were specifically targeted by gold nanoparticles and illuminated by only a few pulses, undergo either necrosis or apoptosis in a highly controlled manner. We also find that at very specific exposure levels, effective fusion between neighboring cells can be induced, a process which could be useful for a range of applications in cancer therapy and drug production.