Any living systems that are electrically excitable simultaneously induce a magnetic field. The superconducting quantum interference device (SQUID), has so far been employed to detect biomagnetic activity. However, this sensor system is too large and expensive for personal and single laboratory use. In order to enable to measure biomagnetic fields in many research labs and clinics, we have improved the sensitivity of a pulse-driven magnetoimpedance (PMI) sensor toward toward a pico-Tesla (pT) level. Since the sensor head is a product of only small electromagnetic parts such as a pickup coil with a small CoFeSiB amorphous wire, it is operated at body temperature and is made as a small electric chip, which can be mounted in a mobile phone and used as a motion sensor of the operation handle in computer games. The excitation pulse (5V, 50-100 ns) is applied to the magnetic amorphous wire at ~1-2 μs intervals. Thus, this sensor enables quasi real time measurements. Here, we show examples of applications of PMI sensors to physiological and medical studies. All animal experiments were carried out in accordance with the Animal Experimental Guides of Nagoya University. Animals (guinea-pigs) were sacrificed by cervical dislocation after anaesthetising with diethyl ether. Also, in human study, procedures were approved by the Institutional Ethics Committee. Written informed consent was obtained from all participants. This study complies with the Declaration of Helsinki. First, we applied this magnetic sensor to measure biomagnetic fields in small tissues isolated from the stomach, taenia caeci, portal vein, and urinary bladder of guinea-pigs. Spontaneous electric activities were recorded by the sensor head mounted ~1 mm below the samples across a cover glass. In gastric musculatures, spontaneous magnetic activity was simultaneously measured with extracellular electric activity, indicating that the biomagnetic field measurements reflected pacemaker electric activity. In addition, spike-like magnetic activities were observed in the presence of K+ channels blockers. Next, we measured magnetic fields on the surface of human chest. Spontaneous magnetic activity was simultaneously measured with electric cardiogram. The magnetic activity was maximal in the 4th intercostals near the center of the sterna. Furthermore, averaging the magnetic activity demonstrated magnetic waves mimicking the P wave and QRS complex. Lastly, we introduce new pulse-driven MI systems. Instead of a sample-hold circuit, fast AD/DA converters were used to sample the whole induction decay in the detector coil. Thus, this system can be used as a DC amplifier of magnetic sensor. Possible numerous applications are suggested.