Sheep zygotes were cultured in serum-free or serum-supplemented media to determine effects on blastocyst yields and within-blastocyst abundance and distribution of neutral lipid droplets. Embryos cultured in synthetic oviduct fluid supplemented with bovine serum albumin (0.4% w/v) (SBSA) generated similar blastocyst yields (mean +/- s.e.m. = 20% +/- 5) to those in synthetic oviduct fluid supplemented with serum (10% v/v) from ewes fed a diet containing 0% (SZFO; 26% +/- 2) or 3% fish oil (S3FO; 23% +/- 3). SBSA zygotes generated more good-quality blastocysts than their SZFO or S3FO counterparts (P < 0.05). Within-blastocyst abundance of neutral lipid droplets was non-uniform; data were collected from discrete embryo sectors (each = 2700 microm2) representing highest (H), intermediate (I) and lowest (L) densities of accumulation. For all sectors, area (microm2) occupied by lipid droplets in SBSA blastocysts (mean H = 470; I = 370; L = 245) was smaller (P < 0.01) than occupied in others (SBSA : SZFO = 1 : 1.41, 1 : 1.48 and 1 : 1.42; SBSA : S3FO = 1 : 1.36, 1 : 1.30 and 1 : 1.31; data for H, I and L, respectively). Among S3FO blastocysts only, inferior quality was associated with greater lipid abundance. Overall, embryo culture in the presence of serum increased neutral lipid droplet abundance but accumulation was non-uniform.