The activation of sphalerite by some metal salts has been briefly reviewed and the influence of lead nitrate on sphalerite in the presence of potassium ethyl xanthate has been investigated by a combination of batch flotation tests and solution analyses on pulps containing a mixture of sphalerite and quartz. The effect of lead addition, of pH and of complexant on the flotation behaviour has led to the conclusion that in mildly acidic conditions the activating entity is lead ion whereas in mildly alkaline conditions the activating entity is lead hydroxide. Some comparisons between lead activated sphalerite and galena have been made. The consequences of these findings in the separation of galena from sphalerite in practical flotation have been briefly discussed.