During two 60-meter saturation dives, U.S. Navy divers hand-collected samples of marine snow (aggregates) and of surrounding water, and made video recordings of aggregates passing through a loop used to determine their sizes and numbers. Analyses of the video recordings revealed that aggregates were abundant during both dives, accounting for 748 and 759 ml per cubic meter of seawater volume respectively. Although the total volume of aggregate material was similar, it was distributed quite differently between the two dives in 220 larger (mean volume 3.40 ml) and 595 smaller (mean volume 1.28 ml) aggregates per cubic meter. Laboratory analyses revealed that many of the aggregate samples were luminous, emitting light from two to six orders-of-magnitude greater than that produced in comparable volumes of the surrounding water. We estimated the total light flux (1)(t) per cubic meter of seawater(l.l x 109 and 3.2 x 108 quanta per second), as well as the portion of that flux which was due to the aggregates. For the two dives, 63 and 20 per cent of the aggregate samples were luminous accounting for 97 and 44 per cent of the total light flux qb(t). These results indicate that marine snow is a variable source for light-scattering material and bioluminescence in the sea.