Seminal leucocytes (WBC) play an important role, whereas this is still unknown. Quantitative normal threshold-value for leucocytospermia (Ls) (WBC < or = 1 million/ml) seems not to be a safety predictive marker of male accessory gland infection (MAGI) and/or MAGI-related adverse effects on semen quality and/or fertility because several drawbacks: a) inadequate staining techniques are responsible of an underestimated WBC concentration in spermatic fractions (100%) obtained from high-density Percoli gradient (Pc 100%); b) Ls could be correlated far better to the clinical findings and/or outcomes if some biochemical data on L metabolism are also studied (Radical Oxygen Species-ROS-generation, phagocytosis, leucotoxins). In order to point out importance about an joint morphological/biochemical analysis about Ls, we recruited 76 selected infertile (from 2-7 yrs) patients (aged 32-45 yrs) who, in their 50% Percoli fractions, had previously produced WBC-ROS > 95th percentile values registered from our control group (n = 28, fertile men). In all infertile population we have analysed through Pc100 fraction either the percentage of WBC-negative patient's specimens (group A) and within WBC-positive ones if a significant difference was present in the maximal WBC-ROS production among different subgroups at WBC concentrations (group B:0.01-0.09, group C:1-10, group D: > 10 x 10(4) WBC/10(7) spermatozoa).(ABSTRACT TRUNCATED AT 250 WORDS)