A series of experiments was conducted to evaluate plasminogen activator production and effects of supplementing culture medium with plasminogen or plasmin on development of rabbit embryos in vitro. In Expt 1, 495 one- to two-cell embryos were cultured in Ham's F-12 with 15 mg BSA ml-1 containing 0, 30, 60 or 120 micrograms porcine plasminogen ml-1 or 0, 75, 150 or 300 micrograms rabbit plasminogen ml-1. Percentages of embryos developing to the expanded blastocyst, hatching blastocyst and hatched blastocyst stages were greater (P < 0.05) in medium with 120 micrograms porcine plasminogen ml-1 than in the absence of plasminogen. More (P < 0.05) embryos developed to the blastocyst, expanded blastocyst and hatching blastocyst stages in medium with 300 micrograms rabbit plasminogen ml-1 than in the absence of plasminogen. In Expt 2, 216 one- to two-cell embryos were cultured in medium with 0, 30, 60 or 120 micrograms porcine plasminogen ml-1 for 96 h, fixed and strained with haematoxylin and eosin, and the number of cells determined. No differences (P > 0.05) were observed in number of cells of morulae but blastocysts developing in medium with 120 micrograms porcine plasminogen ml-1 had more (P < 0.05) cells (109.9 +/- 10.4) than did blastocysts in medium with either 0 (69.4 +/- 14.6) or 30 micrograms porcine plasminogen ml-1 (73.3 +/- 12.2). In Expt 3, 144 one- to two-cell embryos were cultured in medium with 0, 13 or 45 micrograms porcine plasmin ml-1 or 120 micrograms porcine plasminogen ml-1.(ABSTRACT TRUNCATED AT 250 WORDS)