The retinas of a rhesus monkey were exposed to mode-locked visible laser pulses operated under the following exposure conditions: pulse train duration, lOmsecj pulse width, ∽250 psec; pulse repetition rate,∽104 mHz; wavelength, 514.5 nm. Two threshold levels were determined on the basis of ophthalmoscopically observed lesions at one hour post treatment and at 24 hours post treatment. One hour lesion threshold was∽430 mW peak pulse power and 24 hour lesion threshold was ∽210 mW peak pulse power. A grid of 16 exposures ranging from 282 to 1587 mW were placed in the macula region of the retina with adjacent marker lesions used for co-ordinate calibration. After six months post treatment, the animal was sacrificed and perfused with 3% glutaraldehyde in 0.1 M sodium cacodylate buffer. The eyes were post fixed in buffered 1% osmium tetroxide, dehydrated and embedded in Spurr plastic.