With advances in molecular biology and gene cloning techniques, it is now possible to selectively stimulate living cells of interest by using an external light source. This is done by transfecting the cells of interest with a plasmid carrying the channelrhodopsin (ChR2) gene. By stimulating these transfected cells with laser, the light-sensitive ion channels ChR2 are opened, followed by an influx of cation resulting in cell activation. This combination of optical and genetic technique is known in the literature as optogenetics. It is particularly useful in the functional studies of excitable cells, such as neurons, muscle and endocrine cells, to mimic the stimulation from action potentials to trigger the release neurotransmitters and hormones. Here, we describe the methods needed to make selected mammalian cells (PC12) respond to light excitation.