Many factors have been cited as possible reasons for the decline in the number of wild dogs (Lycaon pictus), but few studies have provided supportive data. Between 1990 and 1993, the dynamics of 10 wild dog packs in the southern district of the Kruger National Park in South Africa were monitored. Casual observations of the causes of disease and mortality in the entire population were also recorded. During the same period, 46 wild dogs were immobilised, weighed, and subjected to physical examination as well as the collection of blood and faecal specimens. External parasites were collected and blood smears were prepared. Serum specimens were subjected to routine blood chemistry analyses, hormone and serological assays and formalinised blood specimens and faeces were subjected to screening for endoparasites. The study population varied from 75 in 1990 to 123 in 1993 with a survival rate of 29.9% for pups, 64.3% for yearlings and 69% for adults. Eighty per cent or more of the population were under 4 years of age. The cause of death in all wild dogs in the Kruger National Park could be established only in a small number of cases. Lions were responsible for the death of 20/62 wild dogs and disease caused the death of 6/62 wild dogs. All immobilised dogs were in a good physical condition, but 85% of dogs had one or more skin lesions. Potential life-threatening lesions (bitewounds inflicted by other dogs and lesions inflicted by a snare) occurred in 4 dogs. One male dog had only one testicle in the scortum. Twenty-six (93%) blood smears were positive for gametocytes of Hepatozoon sp., presumably H. canis, and in 2 dogs trophozoites of Babesia canis were seen. Eighty-six per cent of the specimens were positive for Dipetalonema reconditum. All dogs were infested with ticks and Haemaphysalis leachi, Amblyomma hebraeum, A. marmoreum, Boophilus decoloratus, Rhipicephalus simus, R. evertsi, R. appendiculatus and R. zambesiensis were identified. Ctenocephalides sp. and Echidnophaga larina were also identified. Taenia sp., Toxascaris canis and Ancylostoma caninum were present in faecal specimens. Antibody titres to adenovirus (26/31), B. canis (6/15), canine para-influenza virus (21/31), coronavirus (20/31), Coxiella burnetti (8/29), reovirus Type 3 (9/31), Rickettsia conori/africae (27/29), rotavirus (16/31) and Toxoplasma gondii (16/16) were found. The average serum urea concentration was higher (16.4 mmol/e) than that described for captive wild dogs, but other biochemical parameters were generally in agreement with values reported for captive wild dogs.(ABSTRACT TRUNCATED AT 400 WORDS)