Perikinetic coagulation experiments are reported which were performed under 1g and Β΅g conditions during a flight in a sounding rocket, for dispersions of polystyrene, quartz, and amorphous silica particles. Coagulation rates for dispersions of polystyrene, quartz, and amorphous silica are found to increase significantly under Β΅g conditions compared to 1g conditions. Another set of experiments was performed at 1g, 2g, 4g, and 7g, with different densities of the continuous phase; also a mixture of two different polystyrene latices was used. The most pronounced effect of gravity on coagulation rate is found for dispersions with a small density difference, on going from 1g to 2g. In this regime a significant decrease in coagulation rates is observed. For the latex mixture at pronounced density differences, gravity-induced coagulation was observed; however, the aggregates formed did not have a lasting contact. The rate constant calculated under Β΅g conditions approaches the theoretical value of von Smoluchowski. By means of a video analysis of the perikinetic coagulation process, the formation of doublets was studied. The "interaction time" for two particles was found to be longer for the density-matched dispersion. Doublets of particles are easily disrupted, and at 1g, free convection currents were observed even at small temperature differences in the system. Copyright 1998 Academic Press.