Harmful micro- and macroscopic effects of the environmental xenoestrogen p-nonylphenol (p-NP) on the male rat reproductive system have been previously reported. In our study, biochemical evidence of epididymal involvement was sought by determining epididymal marker values after exposure at levels below (5, 20 and 50 mg kg-1) and above (100, 250 and 400 mg kg-1) the "no observed adverse effect" level (NOAEL: 50 mg kg-1 day-1). Exposure to p-NL below the NOAEL did not affect biochemical marker values. At levels above the NOAEL, biochemical markers of epididymal function were affected by the exposure of adults, and by maternal exposure (gestational and lactational periods followed by oral exposure until sexual maturity). l-carnitine was unchanged at all levels of exposure. Exposure of adult males to levels above the NOAEL resulted in higher alpha-glucosidase, suggesting increased epididymal secretory activity. This could upset the balance between secretory and reabsorptive function, and could alter the biochemical composition of the epididymal luminal fluid surrounding spermatocytes during the maturation process. Maternal exposure at levels above the NOAEL resulted in higher tartrate-resistant acid phosphatase activity in the caput-corpus epididymidis, which could indicate an oestrogen-mimicking effect.