The present study assessed the effects of using Improvac (Pfizer Animal Health, Germany) on growth performance and meat characteristics in cross-bred male pigs. In addition average daily weight gain of immunised and surgically castrated males was estimated in order to demonstrate differences in growing patterns in these two treatment groups. The study was carried out in two identical batches. Pigs within batches (n = 446) were allocated to two different treatment groups: immunisation (IM) versus surgical castration (CM). Within treatment groups pigs were randomly assigned to two different diets (low- and high-lysine diet) in order to examine interactions of growth performance and castration technique. Vaccination was performed on the day of entry to the fattening unit and four to six weeks prior to slaughter. At the second vaccination IM-pigs showed significantly lower body weights than the control group (p < 0.05) in both batches. Throughout the whole fattening period CM-pigs tended to have a higher feed intake than IM-pigs while IM-pigs had a significantly lower (better) feed conversion ratio than CM-pigs (p < 0.05).The different lysine content of the diets had no coherent effect on any of the growth performance parameters analysed. Immunised pigs of both feeding groups and in both batches showed a tendency towards a lower carcass weight, back fat values and dressing percentages than surgically castrated pigs.The castration technique had no significant effect on meat quality parameters such as drip loss, shear force or cooking loss while intramuscular fat content (IMF) in immunised pigs fed high-lysine diets (IM(high)) tended to be higher than IMF in immunised pigs fed low-lysine diets (IM(low)). This effect was not seen in surgical castrates in either batch. Immunisation against GnRH offers a good approach to produce taint-free pork while ensuring boar-like growth for a large part of the fattening period.