We analyse the effects of input price discrimination in the canonical model where an upstream monopolist sells to downstream firms with various degrees of efficiency. We first recast a series of existing results within our setting, extending previous findings related to discrimination in final-goods markets to the case of discrimination in input markets. Then, we examine the impact of input price discrimination on welfare. A key determinant of the effects of input price discrimination corresponds to the sum of demand curvature and pass-through elasticity. We provide examples relying on derived demands with constant curvature, including demands with constant pass-through rates.