Abstract
The onset of spermatogenesis in relation to age, bodyweight and testes weight in 105 marmosets used in safety studies has been reviewed. The histological recognition of adverse effects on spermatogenesis is an important part of these studies and this survey indicates that male marmosets should be at least 50 weeks and preferably 60 weeks of age if an assessment of all stages of spermatogenesis is required for safety evaluation.