In the last decade, high-intensity pulsed electric fields with nanosecond durations (3-300 ns) have found breakthrough biomedical applications, e.g., in cancer treatment and gene therapy; however, the physical mechanisms underlying the interaction between nanosecond pulsed electric fields (nsPEFs) and cells, tissues, or organs are not yet fully elucidated. The precise knowledge of the electromagnetic dose received by the exposed sample at the macroscopic, and better still at the microscopic scale, is essential to complete our understanding of the phenomena involved and for adequate interpretation and reproducibility of the results. In this paper, we report a dosimetric and microdosimetric study of an in vitro exposure setup based on a transverse electromagnetic (TEM) cell that allows the exposure of cells in a Petri dish to nsPEFs. The rectangular and bipolar pulses delivered to the cells had a total duration of 1.2 ns and an amplitude of 2 kV. The electric field in situ was characterized experimentally with a nonmetallic probe and numerically using a finite-difference time-domain algorithm. Results of real-time monitoring of temperature were obtained at the subcellular level by using microfluorimetry, which is a method of imaging temperature by using a fluorescent molecular probe with thermosensitive properties.