For marine environments where aggregates are composed of greater than or equal to 50% organic matter, various parameters relevant to aggregation are quantified and compared with those in other aggregation regimes. Some possible environmental effects of the rheological properties of marine organic aggregates are reviewed. The interaction between shear forces in the water and aggregate rheology is likely to determine: firstly, the sinking speed of aggregates and hence vertical organic flux rates; secondly, the volume of microzones, with implications for equilibria and kinetics of chemical reactions in the pelagic milieu; and thirdly, the degree of turbulence damping between aggregates, due to absorption of energy through viscous dissipation inside viscoelastic aggregates during their deformation. Some preliminary results are given of the rheological properties of some laboratory-produced marine organic aggregates.