In the first section aspects of sub-cellular fractionation and estimation of photosynthetically active particles, phycobilisomes, carotenoids, lipids, DNA, RNA, proteins and peptides are discussed. The second section is devoted to the analysis of physiological processes namely transport and assimilation of ammonia, phosphate, nitrate and water (Solutes), and primary photochemical activity and CO2 fixation. A variety of toxins of planktonic algae affect the ecosystem balance and human/animal life and the third section illustrates the procedures for their determination. Since microalgae can sense and respond to toxic anthropogenic compounds like heavy metals, the application of various indicatory/sequestering bioassays is the highlight of the fourth section.