Experiments were carried out to achieve fertilization (IVF) and initial embryonic development of goat oocytes in vitro. Oocyte/cumulus complexes were recovered from large follicles (greater than 7 mm) of hormonally treated doses and from 1-6-mm follicles of ovaries from hormonally superstimulated and nontreated goats. Three different sperm treatment/IVF media were used: defined medium (Brackett and Oliphant, Biol Reprod 1975; 12:260-274) with modifications (mDM); TALP (Bavister and Yanagimachi, Biol Reprod 1977; 16:228-237), as modified by Parrish et al. (Theriogenology 1986; 25:591-600), i.e. modified TALP (mTALP); and HEPES-buffered M199 with modifications (mH-M199). Immature oocytes (from 1-6 mm, small antral follicles) were cultured for in vitro maturation (IVM) in M199 buffered with bicarbonate and with modifications including supplementation with 20% (v/v) goat serum (mB-M199) with either (a) 100 micrograms LH/ml, (b) 5 micrograms FSH/ml, or (c) no added gonadotropin control. Insemination of (in vivo or in vitro) matured oocytes was performed with swim-up separated and heparin-treated freshly ejaculated sperm; additionally, caffeine was included in the mDM treatment. Use of mDM yielded better results than mTALP or mH-M199 (p less than .05). Results with oocytes after IVM were significantly better than those obtained with oocytes matured in vivo (68.4% vs. 45.5%, p less than 0.05). Presence of LH or FSH during oocyte maturation improved both the IVM and IVF results over those of the control (p less than 0.05). The highest proportion of fertilized oocytes (fertilization rate) was achieved by combining the use of mDM for sperm and IVF with IVM in the presence of LH.(ABSTRACT TRUNCATED AT 250 WORDS)