A collar injury of young, field coffee plants at the soil level has been observed occasionally in the summer. The location of the abnormality and the season when it appears .suggested that excessive heating of the soil surface by the sun rays could be its cause. Two experiments were then conducted in the laboratory to investigate this bypothesis. The first experiment consisted in circulating water at the desired temperature around the stem ofyoung coffee plants, using the same apparatus described in a previous paper. In a second experiment the base of the stem and the soil around it was heated by means of a G. E. 250 watts infrared industrial reflector. By changing the distance between the heat source and the plant, different temperatures at the soil surface could be obtained. The results of the first experiment showed that 4 plants out of o that were treated at 45ºC showed injury; the other 2 plants survived without damage. From 5 plants that were treated at 50ºC, 2 showed injury and 3 died shortly after the treatment. All plants subjected to the temperature treatments at 35°C and 40ºC survived without damage, while those treated at 55ºC and 60ºC, died. In the second experiment, 5 plants out of 18 that were treated at temperatures ranging from 45ºC to 51ºC showed injury similar to that observed in the field. All plants treated at temperatures below 45ºC survived without damage with the exception of one treated al 44°C which died. All treatments above 51°C resulted in the death of the plants. It has been observed in the summer that the soil surface temperatures in the field frequently reaches the 45ºC - 51ºC range or sometimes even exceeds it. The results of the present experiments strongly suggest that coffee collar injury at the soil level as observed in the field is caused by excessive sun heating of the soil surface and stem base.