In this paper the author deals with the question related to the coffee seed drying, with special attention to the effect of the sun radiations on seed viability. Based on the results obtained, the following conclusions were drawn : (a) The sun rays have no specific influence on the viability of hulled coffee seed ; their effect is indirect and related to loss of moisture by the seed. (b) Coffee seed can be dried in the sunlight without loss of viability if the water content does not drop under 8% to 9%. Below this critical level seed germination falls rapidly. (c) The moisture content of coffee seed dried „in the sun may fall to about 7% in a short time with the consequent injury to viability. (d) Under most conditions in the state of São Paulo, dehydration of coffee seed carried out in the shade is never injurious to viability because the final water content in such seed always remain well above the critical minimum.