Seasonal differences in sigma-t (1.8)3 temperature (4.0ºC) and salinity (0.9‰) were observed during February/June 1976 in the vicinity of Ilha Grande off the coast of Brazil Estimates of static and dynamic stability were made through the calculation of Brunt-Vaisala frequencies and Richardson numbers, respectively. Both static and dynamic stability values were larger in February than in June for the same location and suggest a greater column stability in February than in June. Stations located in the northern and western channels of Ilha Grande, however, contained greater density reversals than to the east of the Island. Small scale dispersion studies were made using Rhomamine B dye to determine horizontal diffusion coefficients (K) east of the Island and in an embayment of the Island. The estimate for K was 9X10³ cm² s-1 east of the Island, about 2.6 times greater than the value estimated for the protected embayment.