The aim of this study was to evaluate the use of recombinant luteinizing hormone (rLH) supplementation in an unselected group of IVF patients undergoing follicular stimulation with recombinant follicle stimulating hormone (rFSH) after pituitary down-regulation. Group A comprised 122 cycles administered rFSH and rLH while group B included 331 cycles using rFSH only during the same period of treatment. There was no significant difference in any of the endocrine, embryological and outcome parameters measured. The implantation rate of 14.2% for group A compared with 9.8% for group B showed a positive trend (P = 0.055), but for patients in whom LH concentration was <1.0 IU/l at down-regulation or required excessive FSH stimulation, there was an increased incidence of implantation if rLH was supplemented. It was concluded that the addition of exogenous rLH to an unselected group of 'down-regulated' patients stimulated with rFSH appears to offer little benefit, but in the event of profound LH down-regulation or requirement for excessive exogenous FSH (>2500 IU), the rate of implantation might be improved.