The LH1 light harvesting complex has been purified from a mutant of the photosynthetic bacterium Rhodobacter sphaeroides which synthesizes LH1 as the sole pigment protein. Crystallization trials using polyethylene glycol as the precipitant in the presence of the detergent n-octyl glucoside have resulted in the formation of needle like crystals which diffract beyond 3.5 A and which are relatively resistant to radiation damage. X-ray photographs have established that the crystals belong to the tetragonal system and are probably in space group P4(2)2(1)2. Estimates of the crystal density indicate that the asymmetric unit of the crystals contains two oligomers each with an alpha 6 beta 6 stoichiometry.