I. Theoretical Considerations.- 1. Introduction.- 2. Simple Theoretical Models for Magnetic Interactions with Biological Units.- 3. Basic Concepts Related to Magnetic Fields and Magnetic Susceptibility.- 4. The Vector Character of Field and Gradient and Its Possible Implications for Biomagnetic Experiments and Space Travel.- 5. Rotational Diffusion in a Magnetic Field and Its Possible Magnetobiological Implications.- 6. Distortion of the Bond Angle in a Magnetic Field and Its Possible Magnetobiological Implications.- 7. A Possible Effect of the Magnetic Field Upon the Genetic Code.- II. Effect.